Mr. Justice Blackmun
delivered the opinion of the Court.
This case presents a challenge to a New Jersey statute, 1974 N. J. Laws, c. 25, as violative of the Contract Clause of the United States Constitution. That statute, together with a concurrent and parallel New York statute, 1974 N. Y. Laws, c. 993, repealed a statutory covenant made by the two States in 1962 that had limited the ability of The Port Authority of New York and New Jersey to subsidize rail passenger transportation from revenues and reserves.
The suit, one for declaratory relief, was instituted by appellant United States Trust Company of New York in the Superior Court of New Jersey, Law Division, Bergen County. Named as defendants were the State of New Jersey, its Governor, and its Attorney General. Plaintiff-appellant sued as trustee for two series of Port Authority Consolidated Bonds, as a holder of Port Authority Consolidated Bonds, and on behalf of all holders of such bonds.
After a trial, the Superior Court ruled that the statutory repeal was a reasonable exercise of New Jersey’s police power, and declared that it was not prohibited by the Contract Clause or by its counterpart in the New Jersey Constitution, Art. IV, § 7, ¶ 3. Accordingly, appellant’s complaint was dismissed. 134 N. J. Super. 124, 338 A. 2d 833 (1975). The Supreme Court of New Jersey, on direct appeal and by per curiam opinion, affirmed “substantially for the reasons set forth in the [trial court’s] opinion.” 69 N. J. 253, 256, 353 A. 2d 514, 515 (1976). We noted probable jurisdiction. 427 U. S. 903 (1976).
I
BACKGROUND
A. Establishment of the Port Authority. The Port Authority was established in 1921 by a bistate compact to effectuate “a better co-ordination of the terminal, transportation and other facilities of commerce in, about and through the port of New York.” 1921 N. J. Laws, c. 151, p. 413; 1921 N. Y. Laws, c. 154, p. 493. See N. J. Stat. Ann. §32:1-1 et seq. (1940); N. Y. Unconsol. Laws §6401 et seq. (McKinney 1961). The compact, as the Constitution requires, Art. I, § 10, cl. 3, received congressional consent. 42 Stat. 174.
The compact granted the Port Authority enumerated powers and, by its Art. Ill, “such other and additional powers as shall be conferred upon it by the Legislature of either State concurred in by the Legislature of the other, or by Act or Acts of Congress.” The powers are enumerated in Art. VI. Among them is “full power and authority to purchase, construct, lease and/or operate any terminal or transportation facility within said district.” “Transportation facility” is defined, in Art. XXII, to include “railroads, steam or electric, . . . for use for the transportation or carriage of persons or property.”
The Port Authority was conceived as a financially independent entity, with funds primarily derived from private investors. The preamble to the compact speaks of the “encouragement of the investment of capital,” and the Port Authority was given power to mortgage its facilities and to pledge its revenues to secure the payment of bonds issued to private investors.
See generally E. Bard, The Port of New York Authority (1942).
B. Initial Policy Regarding Mass Transit. Soon after the Port Authority’s inception, the two States, again with the consent of Congress, 42 Stat. 822, agreed upon a comprehensive plan for the entity’s development. 1922 N. J. Laws, c. 9; 1922 N. Y. Laws, c. 43. This plan was concerned primarily, if not solely, with transportation of freight by carriers and not with the movement of passengers in the Port Authority district. The plan, however, was not implemented. The New Jersey Legislature at that time declared that the plan “does not include the problem of passenger traffic,” even though that problem “should be considered in co-operation with the port development commission.” 1922 Laws, c. 104. The Port Authority itself recognized the existence of the passenger service problem. 1924 Annual Report 23; 1928 Annual Report 64-66; App. 574a-575a.
In 1927 the New Jersey Legislature, in an Act approved by the Governor, directed the Port Authority to make plans “supplementary to or amendatory of the comprehensive plan ... as will provide adequate interstate and suburban transportation facilities for passengers.” 1927 Laws, c. 277. The New York Legislature followed suit in 1928, but its bill encountered executive veto. The trial court observed that this veto “to all intents and purposes ended any legislative effort to involve the Port Authority in an active role in commuter transit for the next 30 years.” 134 N. J. Super., at 149, 338 A. 2d, at 846.
C. Port Authority Fiscal Policy. Four bridges for motor vehicles were constructed by the Port Authority. A separate series of revenue bonds was issued for each bridge. Revenue initially was below expectations, but the bridges ultimately accounted for much of the Port Authority’s financial strength. The legislatures transferred the operation and revenues of the successful Holland Tunnel to the Port Authority, and this more than made up for the early bridge deficits.
The States in 1931 also enacted statutes creating the general reserve fund of the Port Authority. 1931 N. J. Laws, c. 5; 1931 N. Y. Laws, c. 48. Surplus revenues from all Port Authority facilities were to be pooled in the fund to create an irrevocably pledged reserve equal to one-tenth of the pax value of the Port Authority’s outstanding bonds. This level was attained 15 years later, in 1946.
In 1952, the Port Authority abandoned the practice of earmarking specific facility revenues as security for bonds of that facility. The Port Authority’s Consolidated Bond Resolution established the present method of financing its activities; under this method its bonds are secured by a pledge of the general reserve fund.
D. Renewed Interest in Mass Transit. Meanwhile, the two States struggled with the passenger transportation problem. Many studies were made. The situation was recognized as critical, great costs were envisioned, and substantial deficits were predicted for any mass transit operation. The Port Authority itself financed a study conducted by the Metropolitan Rapid Transit Commission which the States had established in 1954.
In 1958, Assembly Bill No. 16 was introduced in the New Jersey Legislature. This would have had the Port Authority take over, improve, and operate interstate rail mass transit between New Jersey and New York. The bill was opposed vigorously by the Port Authority on legal and financial grounds. The Port Authority also retaliated, in a sense, by including a new safeguard in its contracts with bondholders. This prohibited the issuance of any bonds, secured by the general reserve fund, for a new facility unless the Port Authority first certified that the issuance of the bonds would not “materially impair the sound credit standing” of the Port Authority. App. 812a. Bill No. 16 was not passed.
In 1959, the two States, with the consent of Congress, Pub. L. 86-302, 73 Stat. 575, created the New York-New Jersey Transportation Agency to deal “with matters affecting public mass transit within and between the 2 States.” 1959 N. J. Laws, c. 13, § 3.1, as amended by c. 24; 1959 N. Y. Laws, c. 420, § 3.1.
Also in 1959, the two States enacted legislation providing that upon either State’s election the Port Authority would be authorized to purchase and own railroad passenger cars for the purpose of leasing them to commuter railroads. 1959 N. J. Laws, c. 25; 1959 N. Y. Laws, c. 638. Bonds issued for this purpose would be guaranteed by the electing State. New York so elected, N. Y. Const., Art. X, § 7, effective January 1, 1962, and approximately $100 million of Commuter Car Bonds were issued by the Port Authority to purchase about 500 air-conditioned passenger cars and eight locomotives used on the Penn Central and Long Island Railroads.
E. The 1962 Statutory Covenant. In 1960 the takeover of the Hudson & Manhattan Railroad by the Port Authority was proposed. This was a privately owned interstate electric commuter system then linking Manhattan, Newark, and Hoboken through the Hudson tubes. It had been in reorganization for many years, and in 1959 the Bankruptcy Court and the United States District Court had approved a plan that left it with cash sufficient to continue operations for two years but with no funds for capital expenditures. In re Hudson & Manhattan R. Co., 174 F. Supp. 148 (SDNY 1959), aff'd sub nom. Spitzer v. Stichman, 278 F. 2d 402 (CA2 1960). A special committee of the New Jersey Senate was formed to determine whether the Port Authority was “fulfilling its statutory duties and obligations,” App. 605a. The committee concluded that the solution to bondholder concern was “ [1] imiting by a constitutionally protected statutory covenant with Port Authority bondholders the extent to which the Port Authority revenues and reserves pledged to such bondholders can in the future be applied to the deficits of possible future Port Authority passenger railroad facilities beyond the original Hudson & Manhattan Railroad system.” Id., at 656a. And the trial court found that the 1962 New Jersey Legislature “concluded it was necessary to place a limitation on mass transit deficit operations to be undertaken by the Authority in the future so as to promote continued investor confidence in the Authority.” 134 N. J. Super., at 178, 338 A. 2d, at 863-864.
The statutory covenant of 1962 was the result. The covenant itself was part of the bistate legislation authorizing the Port Authority to acquire, construct, and operate the Hudson & Manhattan Railroad and the World Trade Center. The statute in relevant part read:
“The 2 States covenant and agree with each other and with the holders of any affected bonds, as hereinafter defined, that so long as any of such bonds remain outstanding and unpaid and the holders thereof shall not have given their consent as provided in their contract with the port authority, (a) . . . and (b) neither the States nor the port authority nor any subsidiary corporation incorporated for any of the purposes of this act will apply any of the rentals, tolls, fares, fees, charges, revenues or reserves, which have been or shall be pledged in whole or in part as security for such bonds, for any railroad purposes whatsoever other than permitted purposes hereinafter set forth.” 1962 N. J. Laws, c. 8, § 6; 1962 N. Y. Laws, c. 209, § 6.
The “permitted purposes” were defined to include (i) the Hudson & Manhattan as then existing, (ii) railroad freight facilities, (iii) tracks and related facilities on Port Authority vehicular bridges, and (iv) a passenger railroad facility if the Port Authority certified that it was “self-supporting” or, if not, that at the end of the preceding calendar year the general reserve fund contained the prescribed statutory amount, and that all the Port Authority’s passenger revenues, including the Hudson & Manhattan, would not produce deficits in excess of “permitted deficits.”
A passenger railroad would be deemed “self-supporting” if the amount estimated by the Authority as average annual net income equaled or exceeded the average annual debt service for the following decade. Though the covenant was not explicit on the point, the States, the Port Authority, and its bond counsel have agreed that any state subsidy might be included in the computation of average annual net income of the facility.
“Permitted deficits,” the alternative method under permitted purpose (iv), was defined to mean that the annual estimated deficit, including debt service, of the Hudson tubes and any additional non-self-sustaining railroad facility could not exceed one-tenth of the general reserve fund, or 1% of the Port Authority’s total bonded debt.
The terms of the covenant were self-evident. Within its conditions the covenant permitted, and perhaps even contemplated, additional Port Authority involvement in deficit rail mass transit as its financial position strengthened, since the limitation of the covenant was linked to, and would expand with, the general reserve fund.
A constitutional attack on the legislation containing the covenant was promptly launched. New Jersey and New York joined in the defense. The attack proved unsuccessful. Courtesy Sandwich Shop, Inc. v. Port of New York Authority, 12 N. Y. 2d 379, 190 N. E. 2d 402, appeal dismissed, 375 U. S. 78 (1963). See Kheel v. Port of New York Authority, 331 F. Supp. 118 (SDNY 1971), aff’d, 457 F. 2d 46 (CA2), cert. denied, 409 U. S. 983 (1972).
With the legislation embracing the covenant thus effective, the Port Authority on September 1, 1962, assumed the ownership and operating responsibilities of the Hudson & Manhattan through a wholly owned subsidiary, Port Authority Trans-Hudson Corporation (PATH). Funds necessary for this were realized by the successful sale of bonds to private investors accompanied by the certification required by § 7 of the Consolidated Bond Resolution that the operation would not materially impair the credit standing of the Port Authority, the investment status of the Consolidated Bonds, or the ability of the Port Authority to fulfill its commitments to bondholders. This § 7 certification was based on a projection that the annual net loss of the PATH system would level off at about $6.6 million from 1969 to 1991. At the time the certification was made the general reserve fund contained $69 million, and thus the projected PATH deficit was close to the level of “permitted deficits” under the 1962 covenant. 134 N. J. Super., at 163, and n. 27, 338 A. 2d, at 855, and n. 27.
The PATH fare in 1962 was 30 cents and has remained at that figure despite recommendations for increase. App. 684a-686a. As a result of the continuation of the low fare, PATH deficits have far exceeded the initial projection. Thus, although the general reserve fund had grown to $173 million by 1973, substantially increasing the level of permitted deficits to about $17 million, the PATH deficit had grown to $24.9 million. In accordance with a stipulation of the parties, id., at 682a-683a, the trial court found that the PATH deficit so exceeded the covenant's level of permitted deficits that the Port Authority was unable to issue bonds for any new passenger railroad facility that was not self-supporting. 134 N. J. Super., at 163 n. 26, 338 A. 2d, at 855 n. 26.
F. Prospective Repeal of the Covenant. Governor Cahill of New Jersey and Governor Rockefeller of New York in April 1970 jointly sought increased Port Authority participation in mass transit. In November 1972 they agreed upon a plan for expansion, of the PATH system. This included the initiation of direct rail service to Kennedy Airport and the construction of a line to Plainfield, N. J., by way of Newark Airport. The plan anticipated a Port Authority investment of something less than $300 million out of a projected total cost of $650 million, with the difference to be supplied by federal and state grants. It also proposed to make the covenant inapplicable with respect to bonds issued after the legislation went into effect. This program was enacted, effective May 10, 1973, and the 1962 covenant was thereby rendered inapplicable, or in effect repealed, with respect to bonds issued subsequent to the effective date of the new legislation. 1972 N. J. Laws, c. 208; 1972 N. Y. Laws, c. 1003, as amended by 1973 N. Y. Laws, c. 318.
G. Retroactive Repeal of the Covenant. It soon developed that the proposed PATH expansion would not take place as contemplated in the Governors’ 1972 plan. New Jersey was unwilling to increase its financial commitment in response to a sharp increase in the projected cost of constructing the Plainfield extension. As a result the anticipated federal grant was not approved. App. 717a.
New Jersey had previously prevented outright repeal of the 1962 covenant, but its attitude changed with the election of a new Governor in 1973. In early 1974, when bills were pending in the two States’ legislatures to repeal the covenant retroactively, a national energy crisis was developing. On November 27, 1973, Congress had enacted the Emergency Petroleum Allocation Act, 87 Stat. 627, as amended, 15 U. S. C. § 751 et seq. (1970 ed., Supp. V). In that Act Congress found that the hardships caused by the oil shortage “jeopardize the normal flow of commerce and constitute a national energy crisis which is a threat to the public health, safety, and welfare.” 87 Stat. 628, 15 U. S. C. §751 (a)(3). This time, proposals for retroactive repeal of the 1962 covenant were passed by the legislature and signed by the Governor of each State. 1974 N. J. Laws, c. 25; 1974 N. Y. Laws, c. 993.
On April 10, 1975, the Port Authority announced an increase in its basic bridge and tunnel tolls designed to raise an estimated $40 million annually. App. 405a-407a, 419a-421a, 528a. This went into effect May 5 and was, it was said, “[t]o increase [the Port Authority’s] ability to finance vital mass transit improvements.” Id., at 405a.
II
At the time the Constitution was adopted, and for nearly a century thereafter, the Contract Clause was one of the few express limitations on state power. The many decisions of this Court involving the Contract Clause are evidence of its important place in our constitutional jurisprudence. Over the last century, however, the Fourteenth Amendment has assumed a far larger place in constitutional adjudication concerning the States. We feel that the present role of the Contract Clause is largely illuminated by two of this Court's decisions. In each, legislation was sustained despite a claim that it had impaired the obligations of contracts.
Home Building & Loan Assn. v. Blaisdell, 290 U. S. 398 (1934), is regarded as the leading case in the modern era of Contract Clause interpretation. At issue was the Minnesota Mortgage Moratorium Law, enacted in 1933, during the depth of the Depression and when that State was under severe economic stress, and appeared to have no effective alternative. The statute was a temporary measure that allowed judicial extension of the time for redemption; a mortgagor who remained in possession during the extension period was required to pay a reasonable income or rental value to the mortgagee. A closely divided Court, in an opinion by Mr. Chief Justice Hughes, observed that “emergency may furnish the occasion for the exercise of power” and that the “constitutional question presented in the light of an emergency is whether the power possessed embraces the particular exercise of it in response to particular conditions.” Id., at 426. It noted that the debates in the Constitutional Convention were of little aid in the construction of the Contract Clause, but that the general purpose of the Clause was clear: to encourage trade and credit by promoting confidence in the stability of contractual obligations. Id., at 427-428. Nevertheless, a State “continues to possess authority to safeguard the vital interests of its people. . . . This principle of harmonizing the constitutional prohibition with the necessary residuum of state power has had progressive recognition in the decisions of this Court.” Id., at 434r-435. The great clauses of the Constitution are to be considered in the light of our whole experience, and not merely as they would be interpreted by its Framers in the conditions and with the outlook of their time. Id., at 443.
This Court’s most recent Contract Clause decision is El Paso v. Simmons, 379 U. S. 497 (1965). That case concerned a 1941 Texas statute that limited to a 5-year period the reinstatement rights of an interest-defaulting purchaser of land from the State. For many years prior to the enactment of that statute, such a defaulting purchaser, under Texas law, could have reinstated his claim to the land upon written request and payment of delinquent interest, unless rights of third parties had intervened. This Court held that “it is not every modification of a contractual promise that impairs the obligation of contract under federal law.” Id., at 506-507. It observed that the State “has the ‘sovereign right ... to protect the . . . general welfare of the people’ ” and “ ‘we must respect the “wide discretion on the part of the legislature in determining what is and what is not necessary,” ’ ” id., at 508-509, quoting East New York Savings Bank v. Hahn, 326 U. S. 230, 232-233 (1945). The Court recognized that “the power of a State to modify or affect the obligation of contract is not without limit,” but held that “the objects of the Texas statute make abundantly clear that it impairs no protected right under the Contract Clause.” 379 U. S., at 509.
Both of these cases eschewed a rigid application of the Contract Clause to invalidate state legislation. Yet neither indicated that the Contract Clause was without meaning in modern constitutional jurisprudence, or that its limitation on state power was illusory. Whether or not the protection of contract rights comports with current views of wise public policy, the Contract Clause remains a part of our written Constitution. We therefore must attempt to apply that constitutional provision to the instant case with due respect for its purpose and the prior decisions of this Court.
III
We first examine appellant’s general claim that repeal of the 1962 covenant impaired the obligation of the States’ contract with the bondholders. It long has been established that the Contract Clause limits the power of the States to modify their own contracts as well as to regulate those between private parties. Fletcher v. Peck, 6 Cranch 87, 137-139 (1810); Dartmouth College v. Woodward, 4 Wheat. 518 (1819). Yet the Contract Clause does not prohibit the States from repealing or amending statutes generally, or from enacting legislation with retroactive effects. Thus, as a preliminary matter, appellant’s claim requires a determination that the repeal has the effect of impairing a contractual obligation.
In this case the obligation was itself created by a statute, the 1962 legislative covenant. It is unnecessary, however, to dwell on the criteria for determining whether state legislation gives rise to a contractual obligation. The trial court found, 134 N. J. Super., at 183 n. 38, 338 A. 2d, at 866 n. 38, and appellees do not deny, that the 1962 covenant constituted a contract between the two States and the holders of the Consolidated Bonds issued between 1962 and the 1973 prospective repeal. The intent to make a contract is clear from the statutory language: “The 2 States covenant and agree with each other and with the holders of any affected bonds . . . 1962 N. J. Laws, c. 8, § 6; 1962 N. Y. Laws, c. 209, § 6. Moreover, as the chronology set forth above reveals, the purpose of the covenant was to invoke the constitutional protection of the Contract Clause as security against repeal. In return for their promise, the States received the benefit they bargained for: public marketability of Port Authority bonds to finance construction of the World Trade Center and acquisition of the Hudson & Manhattan Railroad. We therefore have no doubt that the 1962 covenant has been properly characterized as a contractual obligation of the two States.
The parties sharply disagree about the value of the 1962 covenant to the bondholders. Appellant claims that after repeal the secondary market for affected bonds became “thin” and the price fell in relation to other formerly comparable bonds. This claim is supported by the trial court’s finding that “immediately following repeal and for a number of months thereafter the market price for Port Authority bonds was adversely affected.” 134 N. J. Super., at 180, 338 A. 2d, at 865. Appellees respond that the bonds nevertheless retained an “A” rating from the leading evaluating services and that after an initial adverse effect they regained a comparable price position in the market. Findings of the trial court support these claims as well. Id., at 179-182, 338 A. 2d, at 864-866. The fact is that no one can be sure precisely how much financial loss the bondholders suffered. Factors unrelated to repeal may have influenced price. In addition, the market may not have reacted fully, even as yet, to the covenant’s repeal, because of the pending litigation and the possibility that the repeal would be nullified by the courts.
In any event, the question of valuation need not be resolved in the instant case because the State has made no effort to compensate the bondholders for any loss sustained by the repeal. As a security provision, the covenant was not superfluous; it limited the Port Authority’s deficits and thus protected the general reserve fund from depletion. Nor was the covenant merely modified or replaced by an arguably comparable security provision. Its outright repeal totally eliminated an important security provision and thus impaired the obligation of the States’ contract. See Richmond Mortgage & Loan Corp. v. Wachovia Bank & Trust Co., 300 U. S. 124, 128-129 (1937).
The trial court recognized that there was an impairment in this case: “To the extent that the repeal of the covenant authorizes the Authority to assume greater deficits for such purposes, it permits a diminution of the pledged revenues and reserves and may be said to constitute an impairment of the states’ contract with the bondholders.” 134 N. J. Super., at 183, 338 A. 2d, at 866.
Having thus established that the repeal impaired a contractual obligation of the States, we turn to the question whether that impairment violated the Contract Clause.
IV
Although the Contract Clause appears literally to proscribe “any” impairment, this Court observed in Blaisdell that “the prohibition is not an absolute one and is not to be read with literal exactness like a mathematical formula.” 290 U. S., at 428. Thus, a finding that there has been a technical impairment is merely a preliminary step in resolving the more difficult question whether that impairment is permitted under the Constitution. In the instant case, as in Blaisdell, we must attempt to reconcile the strictures of the Contract Clause with the “essential attributes of sovereign power,” id., at 435, necessarily reserved by the States to safeguard the welfare of their citizens. Id., at 434-440.
The trial court concluded that repeal of the 1962 covenant was a valid exercise of New Jersey’s police power because repeal served important public interests in mass transportation, energy conservation, and environmental protection. 134 N. J. Super., at 194-195, 338 A. 2d, at 873. Yet the Contract Clause limits otherwise legitimate exercises of state legislative authority, and the existence of an important public interest is not always sufficient to overcome that limitation. “Undoubtedly, whatever is reserved of state power must be consistent with the fair intent of the constitutional limitation of that power.” Blaisdell, 290 U. S., at 439. Moreover, the scope of the State’s reserved power depends on the nature of the contractual relationship with which the challenged law conflicts.
The States must possess broad power to adopt general regulatory measures without being concerned that private contracts will be impaired, or even destroyed, as a result. Otherwise, one would be able to obtain immunity from state regulation by making private contractual arrangements. This principle is summarized in Mr. Justice Holmes’ well-known dictum: “One whose rights, such as they are, are subject to state restriction, cannot remove them from the power of the State by making a contract about them.” Hudson Water Co. v. McCarter, 209 U. S. 349, 357 (1908).
Yet private contracts are not subject to unlimited modification under the police power. The Court in Blaisdell recognized that laws intended to regulate existing contractual relationships must serve a legitimate public purpose. 290 U. S., at 444-445. A State could not “adopt as its policy the repudiation of debts or the destruction of contracts or the denial of means to enforce them.” Id., at 439. Legislation adjusting the rights and responsibilities of contracting parties must be upon reasonable conditions and of a character appropriate to the public purpose justifying its adoption. Id., at 445-447. As is customary in reviewing economic and social regulation, however, courts properly defer to legislative judgment as to the necessity and reasonableness of a particular measure. East New York Savings Bank v. Hahn, 326 U. S. 230 (1945).
When a State impairs the obligation of its own contract, the reserved-powers doctrine has a different basis. The initial inquiry concerns the ability of the State to enter into an agreement that limits its power to act in the future. As early as Fletcher v. Peck, the Court considered the argument that “one legislature cannot abridge the powers of a succeeding legislature.” 6 Cranch, at 135. It is often stated that “the legislature cannot bargain away the police power of a State.” Stone v. Mississippi, 101 U. S. 814, 817 (1880). This doctrine requires a determination of the State’s power to create irrevocable contract rights in the first place, rather than an inquiry into the purpose or reasonableness of the subsequent impairment. In short, the Contract Clause does not require a State to adhere to a contract that surrenders an essential attribute of its sovereignty.
In deciding whether a State’s contract was invalid ab initio under the reserved-powers doctrine, earlier decisions relied on distinctions among the various powers of the State. Thus, the police power and the power of eminent domain were among those that could not be “contracted away,” but the State could bind itself in the future exercise of the taxing and spending powers. Such formalistic distinctions perhaps cannot be dispositive, but they contain an important element of truth. Whatever the propriety of a State’s binding itself to a future course of conduct in other contexts, the power to enter into effective financial contracts cannot be questioned. Any financial obligation could be regarded in theory as a relinquishment of the State’s spending power, since money spent to repay debts is not available for other purposes. Similarly, the taxing power may have to be exercised if debts are to be repaid. Notwithstanding these effects, the Court has regularly held that the States are bound by their debt contracts.
The instant case involves a financial obligation and thus as a threshold matter may not be said automatically to fall within the reserved powers that cannot be contracted away. Not every security provision, however, is necessarily financial. For example, a revenue bond might be secured by the State’s promise to continue operating the facility in question; yet such a promise surely could not validly be construed to bind the State never to close the facility for health or safety reasons. The security provision at issue here, however, is different : The States promised that revenues and reserves securing the bonds would not be depleted by the Port Authority’s operation of deficit-producing passenger railroads beyond the level of “permitted deficits.” Such a promise is purely financial and thus not necessarily a compromise of the State’s reserved powers.
Of course, to say that the financial restrictions of the 1962 covenant were valid when adopted does not finally resolve this case. The Contract Clause is not an absolute bar to subsequent modification of a State’s own financial obligations. As with laws impairing the obligations of private contracts, an impairment may be constitutional if it is reasonable and necessary to serve an important public purpose. In applying this standard, however, complete deference to a legislative assessment of reasonableness and necessity is not appropriate because the State’s self-interest is at stake. A governmental entity can always find a use for extra money, especially when taxes do not have to be raised. If á State could reduce its financial obligations whenever it wanted to spend the money for what it regarded as an important public purpose, the Contract Clause would provide no protection at all.
The trial court recognized to an extent the special status of a State’s financial obligations when it held that total repudiation, presumably for even a worthwhile public purpose, would be unconstitutional. But the trial court regarded the protection of the Contract Clause as available only in such an extreme case: “The states’ inherent power to protect the public welfare may be validly exercised under the Contract Clause even if it impairs a contractual obligation so long as it does not destroy it.” 134 N. J. Super., at 190, 338 A. 2d, at 870-871.
The trial court’s “total destruction” test is based on what we think is a misreading of W. B. Worthen Co. v. Kavanaugh, 295 U. S. 56 (1935). In the first place, the impairment held unconstitutional in Kavanaugh was one that affected the value of a security provision, and certainly not every bond would have been worthless. More importantly, Mr. Justice Cardozo needed only to state an “outermost limits” test in the Court’s opinion, id., at 60, because the impairment was so egregious. He expressly recognized that the actual line between permissible and impermissible impairments could well be drawn more narrowly. Thus the trial court was not correct when it drew the negative inference that any impairment less oppressive than the one in Kavanaugh was necessarily constitutional. The extent of impairment is certainly a relevant factor in determining its reasonableness. But we cannot sustain the repeal of the 1962 covenant simply because the bondholders’ rights were not totally destroyed.
The only time in this century that alteration of a municipal bond contract has been sustained by this Court was in Faitoute Iron & Steel Co. v. City of Asbury Park, 316 U. S. 502 (1942). That case involved the New Jersey Municipal Finance Act, which provided that a bankrupt local government could be placed in receivership by a state agency. A plan for the composition of creditors’ claims was required to be approved by the agency, the municipality, and 85% in amount of the creditors. The plan would be binding on nonconsenting creditors after a state court conducted a hearing and found that the municipality could not otherwise pay off its creditors and that the plan was in the best interest of all creditors. Id., at 504.
Under the specific composition plan at issue in Faitoute, the holders of revenue bonds received new securities bearing lower interest rates and later maturity dates. This Court, however, rejected the dissenting bondholders’ Contract Clause objections. The reason was that the old bonds represented only theoretical rights; as a practical matter the city could not raise its taxes enough to pay off its creditors under the old contract terms. The composition plan enabled the city to meet its financial obligations more effectively. “The necessity compelled by unexpected financial conditions to modify an original arrangement for discharging a city’s debt is implied in every such obligation for the very reason that thereby the obligation is discharged, not impaired.” Id., at 511. Thus, the Court found that the composition plan was adopted with the purpose and effect of protecting the creditors, as evidenced by their more than 85% approval. Indeed, the market value of the bonds increased sharply as a result of the plan’s adoption. Id., at 513.
It is clear that the instant case involves a much more serious impairment than occurred in Faitoute. No one has suggested here that the States acted for the purpose of benefiting the bondholders, and there is no serious contention that the value of the bonds was enhanced by repeal of the 1962 covenant. Appellees recognized that it would have been impracticable to obtain consent of the bondholders for such a change in the 1962 covenant, Brief for Appellees 97-98, even though only 60% approval would have been adequate. See n. 10, supra. We therefore conclude that repeal of the 1962 covenant cannot be sustained on the basis of this Court’s prior decisions in Faitoute and other municipal bond cases.
V
Mass transportation, energy conservation, and environmental protection are goals that are important and of legitimate public concern. Appellees contend that these goals are so important that any harm to bondholders from repeal of the 1962 covenant is greatly- outweighed by the public benefit. We do not accept this invitation to engage in a utilitarian comparison of public benefit and private loss. Contrary to Mr. Justice Black’s fear, expressed in sole dissent in El Paso v. Simmons, 379 U. S., at 517, the Court has not “balanced away” the limitation on state action imposed by the Contract Clause. Thus a State cannot refuse to meet its legitimate financial obligations simply because it would prefer to spend the money to promote the public good rather than the private welfare of its creditors. We can only sustain the repeal of the 1982 covenant if that impairment was both reasonable and necessary to serve the admittedly important purposes claimed by the State.
The more specific justification offered for the repeal of the 1962 covenant was the States’ plan for encouraging users of private automobiles to shift to public transportation. The States intended to discourage private automobile use by raising bridge and tunnel tolls and to use the extra revenue from those tolls to subsidize improved commuter railroad service. Appellees contend that repeal of the 1962 covenant was necessary to implement this plan because the new mass transit facilities could not possibly be self-supporting and the covenant’s “permitted deficits” level had already been exceeded. We reject this justification because the repeal was neither necessary to achievement of the plan nor reasonable in light of the circumstances.
The determination of necessity can be considered on two levels. First, it cannot be said that total repeal of the covenant was essential; a less drastic modification would have permitted the contemplated plan without entirely removing the covenant’s limitations on the use of Port Authority revenues and reserves to subsidize commuter railroads. Second, without modifying the covenant at all, the States could have adopted alternative means of achieving their twin goals of discouraging automobile use and improving mass transit. Appellees contend, however, that choosing among these alternatives is a matter for legislative discretion. But a State is not completely free to consider impairing the obligations of its own contracts on a par with other policy alternatives. Similarly, a State is not free to impose a drastic impairment when an evident and more moderate course would serve its purposes equally well. In El Paso v. Simmons, supra, the imposition of a five-year statute of limitations on what was previously a perpetual right of redemption was regarded by this Court as “quite clearly necessary” to achieve the State’s vital interest in the orderly administration of its school lands program. 379 U. S., at 515-516. In the instant case the State has failed to demonstrate that repeal of the 1962 covenant was similarly necessary.
We also cannot conclude that repeal of the covenant was reasonable in light of the surrounding circumstances. In this regard a comparison with El Paso v. Simmons, supra, again is instructive. There a 19th century statute had effects that were unforeseen and unintended by the legislature when originally adopted. As a result speculators were placed in a position to obtain windfall benefits. The Court held that adoption of a statute of limitation was a reasonable means to “restrict a party to those gains reasonably to be expected from the contract” when it was adopted. 379 U. S., at 515.
By contrast, in the instant case the need for mass transportation in the New York metropolitan area was not a new development, and the likelihood that publicly owned commuter railroads would produce substantial deficits was well known. As early as 1922, over a half century ago, there were pressures to involve the Port Authority in mass transit. It was with full knowledge of these concerns that the 1962 covenant was adopted. Indeed, the covenant was specifically intended to protect the pledged revenues and reserves against the possibility that such concerns would lead the Port Authority into greater involvement in deficit mass transit.
During the 12-year period between adoption of the covenant and its repeal, public perception of the importance of mass transit undoubtedly grew because of increased general concern with environmental protection and energy conservation. But these concerns were not unknown in 1962, and the subsequent changes were of degree and not of kind. We cannot say that these changes caused the covenant to have a substantially different impact in 1974 than when it was adopted in 1962. And we cannot conclude that the repeal was reasonable in the light of changed circumstances.
We therefore hold that the Contract Clause of the United States Constitution prohibits the retroactive repeal of the 1962 covenant. The judgment of the Supreme Court of New Jersey is reversed.
It is so ordered.
Mr. Justice Stewart took no part in the decision of this case.
Mr. Justice Powell took no part in the consideration or decision of this case.
“No State shall . . . pass any . . . Law impairing the Obligation of Contracts . . . .” U. S. Const., Art. I, § 10, cl. 1.
The name originally was “The Port of New York Authority.” 1921 N. J. Laws, c. 151, p. 416; 1921 N. Y. Laws, c. 154, p. 496. It was changed to “The Port Authority of New York and New Jersey,” effective July 1, 1972. 1972 N. J. Laws, c. 69; 1972 N. Y. Laws, c. 531.
Appellant is trustee for the Fortieth and Forty-first Series of Port Authority Consolidated Bonds, with an aggregate principal amount of $200 million. At the time the complaint was filed, appellant also held approximately $96 million of Consolidated Bonds in its own account, as custodian, and as fiduciary in several capacities. There were then over $1,600 million of Consolidated Bonds outstanding.
The State of New York is not a party to this case, although its Attorney General has filed a brief as amicus curiae. A challenge to the parallel New York statute has been pending in the Supreme Court of New York, County of New York, since 1974. United States Trust Co. of New York v. New York, No. 09128/74.
The Port Authority possessed no taxing power and was unable to pledge the credit of either State. The trial court found:
“Under the terms of the Compact the power to levy taxes or to pledge the credit of either state was expressly withheld from the Authority. From its inception, with the exception of monies advanced as loans by the states, the Authority was required to finance its facilities solely with money borrowed from the public and to be repaid out of the revenues derived from its operations. By reason of these financial limitations two concepts initially emerged which have played an important role in the realization of the purposes for which the Authority was created: first, the specific projects undertaken by the Authority should be self-supporting, i. e., the revenues of each should be sufficient to cover its operating expenses and debt service requirements; and second, since the Authority is a public agency over which its creditors have no direct control, the bondholders should be protected by covenants with the Authority and with the states which have ultimate control over its operations.” 134 N. J. Super. 124, 139-140, 338 A. 2d 833, 841 (1975).
The two States subsequently took steps to protect the Port Authority’s financial integrity. See, for example, the 1925 statutory declarations not to authorize the construction of competitive bridges within the district or to limit the right of the Port Authority to levy such charges and tolls as it deemed necessary to produce revenues to fund its bonds. 1925 N. J. Laws, c. 37, § 5; 1925 N. Y. Laws, c. 210, § 5.
The parties are not in agreement as to the original perception of the compact and the plan. The appellant claims that the Port Authority was organized “as a freight coordinating agency,” Brief for Appellant 5, whereas the appellees challenge that description and emphasize the presence of a mass transit problem as a factor of profound concern in the Port Authority’s development. Brief for Appellees 2-5. The trial court found that neither the commission which recommended the creation of the Port Authority nor the comprehensive plan contemplated responsibility of the agency for passenger transit. 134 N. J. Super., at 134-139, 338 A. 2d, at 838-841.
Governor Alfred E. Smith in his statement in support of his veto said:
“[I]t has been a great disappointment to me to find that the opposition of the railroads has prevented to date the making of real progress in working out the program of freight distribution in the port which always has been the main object and purpose of the Port of New York Authority. I am satisfied that the Port Authority should stick to this program and I am entirely unwilling to give my approval to any measure which at the expense of the solution of the great freight distribution problem will set the Port Authority off on an entirely new line of problem connected with the solution of the suburban passenger problem.” App. 573a-574a.
The appellees state that the creation of the general reserve fund “made the Port Authority's fiscal strength possible." Brief for Appellees 6 n. 7.
The parties, however, are in disagreement as to the actual and proper fiscal policy of the Port Authority. Appellant claims that each facility should have prospects of producing sufficient revenue to support itself. Appellees' position is apparent from their assertion that although the self-supporting-facility concept may have “initially emerged,” as the trial court stated, 134 N. J. Super., at 140, 338 A. 2d, at 841, “the concept had no practical significance because it was not attained prior to 1931 and was unnecessary after 1931,” with the establishment of the general reserve fund. Brief for Appellees 7.
The trial court observed that upon the adoption of the Consolidated Bonds Resolution in 1952, the self-supporting-facility concept “ceased to have the significance previously attached to it.” 134 N. J. Super., at 143, 338 A. 2d, at 843.
Not at issue in the instant ease is part (a) of § 6 of the statutory-covenant (omitted in the quoted material in the text), which promises that the States will not impair the Port Authority’s control over its fees or services. This provision has not been repealed, even prospectively.
Notwithstanding the “permitted deficits” formula, the covenant permits use of Port Authority revenues for mass transit if 60% of the bondholders give their consent. The procedures for obtaining such consent are provided in § 16 (b) of the Consolidated Bond Resolution. App. 802a-809a. The Port Authority commissioned a study by First Boston Corporation in 1971 that proposed placing a surcharge on bridge and tunnel tolls, with the extra revenues going to a special fund to secure bonds for mass transportation projects. This proposal would not have diminished the historic reserves pledged to secure the bonds. The study concluded, however, that some increase in the interest rates of existing bonds would have been necessary to obtain a favorable vote of the bondholders. Id,., at 696a-699a. There is some evidence in the record that such a proposal could not win bondholder approval, partly because the requisite procedures are unwieldy. Id., at 191a-192a.
The introductory statement appended to the New Jersey bill recited:
“The bill is also designed to preclude the application of the 1962 covenant to holders of bonds newly issued after the effective date of this act, while maintaining in status quo the rights of the holders of the bonds issued after March 27, 1962 (the effective date of the 1962 covenant legislation) but prior to the effective date of this act.” Id,., at 707a.
Earlier in 1972 the New York Legislature had enacted, and the Governor had signed, a bill repealing the 1962 covenant in its entirety. 1972 N. Y. Laws, c. 1003. New Jersey did not adopt the necessary complementary legislation at that time. The 1973 amendment to the New York legislation, noted in the text, was then enacted to conform to the New Jersey statute.
Governor Wilson of New York, upon signing that State's repealer, observed:
“It is with great reluctance that I approve a bill that overturns a solemn pledge of the State. I take this extraordinary step only because it will lead to an end of the existing controversy over the validity of the statutory covenant, a controversy that can only have an adverse affect [sic] upon the administration and financing of the Port Authority, and because it will lead to a speedy resolution by the courts of the questions and issues concerning the validity of the statutory covenant. Because it is the province of the courts to decide questions of constitutionality, I will not prevent the covenant issue from being brought before them, especially where it is the unanimously expressed desire of the members of both houses of the New York State Legislature as well as the expressed will of the Governor and both houses of the Legislature of the State of New Jersey to do so.” App. 774a.
The Contract Clause is in the phrase of the Constitution which contains the prohibition against any State’s enacting a bill of attainder or ex post facto law. Notwithstanding Mr. Chief Justice Marshall’s reference to these two other forbidden categories in Fletcher v. Peck, 6 Cranch, at 138-139, it is clear that they limit the powers of the States only with regard to the imposition of punishment. Cummings v. Missouri, 4 Wall. 277, 322-326 (1867); Calder v. Bull, 3 Dall. 386, 390-391 (1798). The Due Process Clause of the Fourteenth Amendment generally does not prohibit retrospective civil legislation, unless the consequences are particularly “harsh and oppressive.” Welch v. Henry, 305 U. S. 134, 147 (1938). See Usery v. Turner Elkhorn Mining Co., 428 U. S. 1, 14-20 (1976).
In general, a statute is itself treated as a contract when the language and circumstances evince a legislative intent to create private rights of a contractual nature enforceable against the State. Compare Dodge v. Board of Education, 302 U. S. 74, 78-79 (1937), with Indiana ex rel. Anderson v. Brand, 303 U. S. 95, 104-105 (1938). In addition, statutes governing the interpretation and enforcement of contracts may be regarded as forming part of the obligation of contracts made under their aegis. See n. 17, infra. .See generally Hale, The Supreme Court and the Contract Clause: II, 57 Harv. L. Rev. 621, 663-670 (1944).
Between the enactment of the 1962 covenant and its retrospective repeal in 1974, the Fort Authority issued and sold to the public $1,260 million of Consolidated Bonds. The Fortieth and Forty-first Series, for which appellant is trustee, were issued after the 1973 prospective repeal and prior to the retrospective repeal. The holders of those bonds were not parties to the 1962 covenant, since the States undoubtedly had the power to repeal the covenant prospectively. See Ogden v. Saunders, 12 Wheat. 213 (1827). The subsequent bondholders arguably are like third-party beneficiaries of the covenant. There is testimony in the record that they were indirectly protected because the bonds outstanding at the time of the prospective repeal (in excess of $1 billion) could not be expected to be retired in the foreseeable future. App. 1105a. We need not decide whether that indirect relationship supports standing to challenge the retroactive repeal, however. Appellant also sued as a holder of Consolidated Bonds (some $72 million) issued between 1962 and 1973. Id., at 56a-57a.
Contract rights are a form of property and as such may be taken for a public purpose provided that just compensation is paid. Contributors to Pennsylvania Hospital v. Philadelphia, 245 U. S. 20 (1917); see El Paso v. Simmons, 379 U. S. 497, 533-534 (1965) (Black, J., dissenting).
The obligations of a contract long have been regarded as including not only the express terms but also the contemporaneous state law per-taming to interpretation and enforcement. “This Court has said that ‘the laws which subsist at the time and place of the making of a contract, and where it is to be performed, enter into and form a part of it, as if they were expressly referred to or incorporated in its terms.’ ” Home Building & Loan Assn. v. Blaisdell, 290 U. S. 398, 429-430 (1934), quoting Von Hoffman v. City of Quincy, 4 Wall. 535, 550 (1867). See also Ogden v. Saunders, 12 Wheat., at 259-260, 297-298 (opinions of Washington and Thompson, JJ.). This principle presumes that contracting parties adopt the terms of their bargain in reliance on the law in effect at the time the agreement is reached.
It is not always unconstitutional, however, for changes in statutory remedies to affect pre-existing contracts. During the early years when the Contract Clause was regarded as an absolute bar to any impairment, this result was reached by treating remedies in a manner distinct from substantive contract obligations. Thus, for example, a State could abolish imprisonment for debt because elimination of this remedy did not impair the underlying obligation. Penniman’s Case, 103 U. S. 714 (1881); Mason v. Haile, 12 Wheat. 370 (1827); see Sturges v. Crowninshield, 4 Wheat. 122, 200-201 (1819).
Yet it was also recognized very early that the distinction between remedies and obligations was not absolute. Impairment of a remedy was held to be unconstitutional if it effectively reduced the value of substantive contract rights. Green v. Biddle, 8 Wheat. 1, 75-76, 84-85 (1823). See also Bronson v. Kinzie, 1 How. 311, 315-318 (1843); Von Hoffman v. City of Quincy, 4 Wall., at 552-554. More recent decisions have not relied on the remedy/obligation distinction, primarily because it is now recognized that obligations as well as remedies may be modified without necessarily violating the Contract Clause. El Paso v. Simmons, 379 U. S., at 506-507, and n. 9; Home Building & Loan Assn. v. Blaisdell, 290 U. S., at 429-435.
Although now largely an outdated formalism, the remedy/obligation distinction may be viewed as approximating the result of a more particularized inquiry into the legitimate expectations of the contracting parties. The parties may rely on the continued existence of adequate statutory remedies for enforcing their agreement, but they are unlikely to expect that state law will remain entirely static. Thus, a reasonable modification of statutes governing contract remedies is much less likely to upset expectations than a law adjusting the express terms of an agreement. In this respect, the repeal of the 1962 covenant is to be seen as a serious disruption of the bondholders’ expectations.
Accord: Stephenson v. Binford, 287 U. S. 251, 276 (1932); Manigault v. Springs, 199 U. S. 473, 480 (1905). See Home Building & Loan Assn. v. Blaisdell, 290 U. S., at 437-438.
Blaisdell suggested further limitations that have since been subsumed in the overall determination of reasonableness. The legislation sustained in Blaisdell was adopted pursuant to a declared emergency in the State and strictly limited in duration. Subsequent decisions struck down state laws that were not so limited. W. B. Worthen Co. v. Thomas, 292 U. S. 426, 432-434 (1934) (relief not limited as to "time, amount, circumstances, or need"); Treigle v. Acme Homestead Assn., 297 U. S. 189, 195 (1936) (no emergency or temporary measure). Later decisions abandoned these limitations as absolute requirements. Veix v. Sixth Ward Building & Loan Assn., 310 U. S., 32, 39-40 (1940) (emergency need not be declared and relief measure need not be temporary); East New York Savings Bank v. Hahn, 326 U. S. 230 (1945) (approving 10th extension of one-year mortgage moratorium). Undoubtedly the existence of an emergency and the limited duration of a relief measure are factors to be assessed in determining the reasonableness of an impairment, but they cannot be regarded as essential in every case.
Stone v. Mississippi sustained the State’s revocation of a 25-year charter to operate a lottery. Other cases similarly have held that a State is without power to enter into binding contracts not to exercise its police power in the future. E. g., Pierce Oil Corp. v. City of Hope, 248 U. S. 498, 501 (1919); Atlantic Coast Line R. Co. v. Goldsboro, 232 U. S. 548, 558 (1914); Douglas v. Kentucky, 168 U. S. 488, 502-505 (1897). See Home Building & Loan Assn. v. Blaisdell, 290 U. S., at 436-437.
In New Jersey v. Wilson, 7 Cranch 164 (1812), the Court held that a State could properly grant a permanent tax exemption and that the Contract Clause prohibited any impairment of such an agreement. This holding has never been repudiated, although tax exemption contracts generally have not received a sympathetic construction. See B. Wright, The Contract Clause of the Constitution 179-194 (1938).
By contrast, the doctrine that a State cannot contract away the power of eminent domain has been established since West River Bridge Co. v. Dix, 6 How. 507 (1848). See Contributors to Pennsylvania Hospital v. Philadelphia, 245 U. S., at 23-24. The doctrine that a State cannot be bound to a contract forbidding the exercise of its police power is almost as old. See n. 20, supra.
State laws authorizing the impairment of municipal bond contracts have been held unconstitutional. W. B. Worthen Co. v. Kavanaugh, 295 U. S. 56 (1935); Louisiana v. Pilsbury, 105 U. S. 278 (1882). Similarly, a tax on municipal bonds was held unconstitutional because its effect was to reduce the contractual rate of interest. Murray v. Charleston, 96 U. S. 432, 443-446 (1878).
A number of cases have held that a State may not authorize a municipality to borrow money and then restrict its taxing power so that the debt cannot be repaid. Louisiana ex rel. Hubert v. New Orleans, 215 U. S. 170, 175-178 (1909); Wolff v. New Orleans, 103 U. S. 358, 365-368 (1881); Von Hoffman v. City of Quincy, 4 Wall., at 554-555. See Fisk v. Jefferson Police Jury, 116 U. S. 131 (1885) (contract for payment of public officer).
See also Wood v. Lovett, 313 U. S. 362 (1941); Indiana ex rel. Anderson v. Brand, 303 U. S. 95 (1938).
“The truth is, States and cities, when they borrow money and contract to repay it with interest, are not acting as sovereignties. They come down to the level of ordinary individuals. Their contracts have the same meaning as that of similar contracts between private persons. Hence, instead of there being in the undertaking of a State or city to pay, a reservation of a sovereign right to withhold payment, the contract should be regarded as an assurance that such a right will not be exercised. A promise to pay, with a reserved right to deny or change the effect of the promise, is an absurdity.” Murray v. Charleston, 96 U. S., at 445.
See El Paso v. Simmons, 379 U. S. 497 (1965); Faitoute Iron & Steel Co. v. City of Asbury Park, 316 U. S. 502 (1942); Louisiana v. New Orleans, 102 U. S. 203 (1880).
For similar reasons, a dual standard of review was applied under the Fifth Amendment to federal legislation abrogating contractual gold clauses. “There is a clear distinction between the power of the Congress to control or interdict the contracts of private parties when they interfere with the exercise of its constitutional authority, and the power of the Congress to alter or repudiate the substance of its own engagements when it has borrowed money under the authority which the Constitution confers.” Perry v. United States, 294 U. S. 330, 350-351 (1935). Cf. Norman v. Baltimore & O. R. Co., 294 U. S. 240, 304-305 (1935). See also Lynch v. United States, 292 U. S. 571, 580 (1934) (need for money is no excuse for repudiating contractual obligations); Note, The Constitutionality of the New York Municipal Wage Freeze and Debt Moratorium: Resurrection of the Contract Clause, 125 U. Pa. L. Rev. 167, 188-191 (1976).
In Kavanaugh, the State changed its statutory procedure for enforcing certain municipal assessments against property owners. The holders of bonds for which the assessments were pledged as security were found to have contract rights in the previous statutory scheme. Without classifying the enforcement statutes as substantive or remedial, the Court held the change unconstitutional because it “[took] from the mortgage the quality of an acceptable investment for a rational investor.” 295 U. S., at 60. In the instant case the State has repudiated an express promise rather than one implied from the statutory scheme in effect at the time of the contract. Thus, the instant case may be regarded as a more serious abrogation of the bondholders’ expectations than occurred in Kavanaugh. See n. 17, supra.
The dissent suggests, post, at 41-44, that such careful scrutiny is unwarranted in this case because the harm to bondholders is relatively small. For the same reason, however, contractual obligations of this magnitude need not impose barriers to changes in public policy. The States remain free to exercise their powers of eminent domain to abrogate such contractual rights, upon payment of just compensation. See n. 16, supra.
If in fact the States sought to divert only new revenues to subsidize mass transit, then the covenant could have been amended to exclude the additional bridge and tunnel tolls from the revenue use limitation that was imposed. Such a change would not have reduced the covenant to a nullity because it would have continued to prevent the diminution of revenues and reserves that historically secured the bonds. And even if the plan contemplated use of current revenues and reserves, the formula for computing “permitted deficits” perhaps could have been modified without totally abandoning an objective limitation on the Port Authority’s involvement in deficit mass transit. Finally, the procedures for obtaining bondholder approval could have been modified so that such consent would present a feasible means of undertaking new projects. See n. 10, supra.
Of course, we express no opinion as to whether any of these lesser impairments would be constitutional.
Transportation control strategies are available that do not require direct application of revenues from bridge and tunnel tolls to subsidize mass transit. In calling for air pollution abatement measures in New Jersey, the Administrator of the Environmental Protection Agency encouraged “close examination” of such measures as, inter alia, “State taxes to encourage VMT [vehicle miles traveled] reductions while raising revenues to benefit mass transit” and realignment of toll structures by “elimination of commuter discounts” and “possibly an increase in tolls during peak commuting times to encourage carpools.” 38 Fed. Reg. 31389 (1973). Thus, the States could discourage automobile use through taxes on gasoline or parking, for example, and use the revenues to subsidize mass transit projects so they would be “self-supporting” within the meaning of the covenant. Bridge and tunnel tolls could be increased for commuters and decreased at other times, so that there would be no excess revenue for purposes of the General Bridge Act of 1946, 33 U. S. C. § 526.
This Court previously has regarded the elimination of unforeseen windfall benefits as a reasonable basis for sustaining changes in statutory deficiency judgment procedures. These changes were adopted by several States when unexpected reductions in property values during the Depression permitted some mortgagees to recover far more than their legitimate entitlement. See Gelfert v. National City Bank, 313 U. S. 221, 233-235 (1941); Honeyman v. Jacobs, 306 U. S. 539, 542-543 (1939); Richmond Mortgage & Loan Corp. v. Wachovia Bank & Trust Co., 300 U. S. 124, 130-131 (1937).