Justice Scalia
delivered the opinion of the Court.
On September 15, 1980, Union Pacific Railroad Co. (UP) and Missouri Pacific Railroad Co. (MP) and their respective corporate parents filed a joint application with the Interstate Commerce Commission (ICC or Commission) seeking permission for UP to acquire control of MP. The same day, a similar but separate application was jointly filed by UP and the Western Pacific Railroad Co. (WP). In a consolidated proceeding, the control applications were opposed by a number of labor organizations, including respondents Brotherhood of Locomotive Engineers (BLE) and United Transportation Union (UTU), as well as several competing railroads, including petitioner Missouri-Kansas-Texas Railroad Co. (MKT) and the Denver and Rio Grande Western Railroad Co. (DRGW). MKT and DRGW, in addition to opposing the mergers, filed responsive applications seeking the right to conduct operations using the track of the new consolidated carrier in the event that the control applications were approved. MKT’s request for trackage rights specified that “MKT, with its own employees, and at its sole cost and expense, shall operate its engines, cars and trains on and along Joint Track.” Proposed Trackage Rights Agreement § 5, Finance Docket No. 30,000 (Sub.-No. 25). DRGW’s application indicated that it “may, at its option, elect to employ its own crews for the movement of its trains, locomotives and cars to points on or over the Joint Track.” Proposed Track-age Rights Agreement § 6(c)(3), Finance Docket No. 30,000 (Sub.-No. 18).
On October 20, 1982, the ICC approved UP’s control acquisitions and granted MKT’s application for trackage rights over 200 miles of MP and UP track in four States and DRGW’s application for rights over 619 miles of MP track between Pueblo and Kansas City. See Union Pacific Corp., Pacific Rail System, Inc. & Union Pacific R. Co.—Control—Missouri Pacific Corp. & Missouri Pacific R. Co., 366 I. C. C. 459 (1982), aff’d sub nom. Southern Pacific Transportation Co. v. ICC, 237 U. S. App. D. C. 99, 736 F. 2d 708 (1984), cert. denied, 469 U. S. 1208 (1985). The approved trackage rights were to become effective “immediately upon consummation of the consolidations.” 366 I. C. C., at 590.
It is the Commission’s standard practice, in pursuit of its statutory responsibility to shield railroad employees from dislocations resulting from actions that it approves, see 49 U. S. C. § 11347, to impose on trackage rights transactions a set of employee protections known as the “NW-BN-Mendocino” conditions. See Norfolk and Western R. Co.—Trackage Rights—Burlington Northern, Inc., 354 I. C. C. 605 (1978), modified, Mendocino Coast R. Co.—Lease and Operate—California Western R. Co., 360 I. C. C. 653 (1980), aff’d sub nom. Railway Labor Executives’ Assn. v. United States, 219 U. S. App. D. C. 23, 675 F. 2d 1248 (1982). These provide, inter alia, for “the selection of forces from all employees involved,” 354 I. C. C., at 610, in transactions involving the dismissal or displacement of employees, and for retention of “[t]he rates of pay, rules, working conditions and all collective bargaining and other rights, privileges and benefits . . . unless changed by future collective bargaining agreements or applicable statutes.” Ibid. The ICC’s October 20, 1982, order indicated, without discussion, that approval of the trackage rights applications was “subject to the imposition of employee protective conditions to the extent specified in [NW-BN and Mendocino] .” 366 I. C. C., at 654. See also id., at 471, 622.
The control transactions among UP, MP, and WP were consummated on December 22, 1982, at which point the grants of trackage rights also became effective. MKT commenced its operations, using its own crews, on or about January 6, 1983; and DRGW shortly thereafter entered into an agreement with MP providing “for using MP crews on [DRGW] trains for a temporary, interim period, after which [DRGW] will operate the trains with [its] own crews.” App. in Nos. 83-2290 and 83-2317 (CADC), p. 6. Although numerous parties, including BLE, had petitioned for review of the Commission’s October 20, 1982, order (which was affirmed in most respects some 18 months later, see Southern Pacific Transportation Co. v. ICC, supra), no question concerning the crewing of MKT or DRGW trains was raised at that time. However, on April 4, 1983, BLE filed with the Commission a “Petition for Clarification,” contending that the Commission had no jurisdiction to, and as a matter of consistent practice did not, inject itself into labor matters such as crew selection, and asking the Commission to declare that its October 20, 1982, order did not have the intent or effect of authorizing the tenant carriers to use their own crews on routes that they had not previously served. In a brief order served May 18, 1983, the Commission denied the petition, ruling that its prior decision “does not require clarification.” App. to Pet. for Cert. in No. 85-793, p. A38. The tenant railroads, it said, had proposed to use their own crews in their trackage rights applications, and “our approval of the applications authorizes such operations.” Ibid.
Within the period prescribed by Commission rules for filing petitions for administrative review, see 49 CFR § 1115.3(e) (1986), both BLE and UTU sought “reconsideration” of the Commission’s denial. In addition to repeating BLE’s earlier arguments, the unions contended that the tenant railroads’ crewing procedures constituted a unilateral change in working conditions forbidden by the NW-BN-Mendocino labor protective conditions, by the Railway Labor Act, 45 U. S. C. § 151 et seq. (RLA), and by collective-bargaining agreements, and that the Commission had made no findings that would justify exempting the trackage rights transactions from applicable labor laws. In a lengthy order served on October 25, 1983, responding in some detail to all of the major contentions, the Commission denied the petitions. In particular, the Commission emphasized its reliance on 49 U. S. C. § 11341(a), which provides that a carrier participating in a consolidation approved by the Commission “is exempt from the antitrust laws and from all other law ... as necessary to let that person carry out the transaction . . . .” The Commission concluded that the exemption provided by this section extends to the RLA and is self-executing, requiring no findings by the Commission to make it effective.
On December 16, 1983, BLE petitioned for judicial review of the May 18, 1983, and October 25, 1983, orders; UTU petitioned for review of the latter order on December 23, 1983. The cases were consolidated, and the United States Court of Appeals for the District of Columbia Circuit vacated both orders. 245 U. S. App. D. C. 311, 761 F. 2d 714 (1985). The court rejected the threshold claim that the appeals were time barred, and concluded on the merits that if the ICC intended to exempt the railroads from the requirements of the RLA, it was required to explain, as it had not done, why that exemption was necessary to effectuate the transactions it approved. The dissent disagreed on both counts.
MKT and the Commission filed petitions for certiorari on the question of the proper construction of § 11841(a), which we granted and consolidated for argument. See 475 U. S. 1081 (1986). We now conclude that the petitions for review must be dismissed.
I
The petitions for review and the Court of Appeals’ order encompass both the May 18, 1983, order refusing to clarify the Commission’s prior approval order, and the October 25, 1983, order refusing to reconsider that refusal to clarify. We consider first the appeal of the latter order.
With certain exceptions not relevant here, see 28 U. S. C. § 1336(b), judicial review of final orders of the ICC is governed by the Hobbs Act, 28 U. S. C. §2341 et seq., which provides that any party aggrieved by a “final order” of the Commission “may, within 60 days after its entry, file a petition to review the order in the court of appeals wherein venue lies.” §2344. A Commission order in a rail proceeding is “final on the date on which it is served.” 49 U. S. C. §10327(i). The Commission’s order refusing to reconsider its refusal to clarify thus became final on October 25, 1983, and the unions’ petitions for review — filed on December 16, 1983, and December 23, 1983 — were therefore timely for purposes of reviewing that order (though they obviously were not timely for purposes of reviewing the original order of October 20, 1982). However, although the timeliness requirements of the Hobbs Act were satisfied, the order from which the unions have appealed is unreviewable.
The Commission’s authority to reopen and reconsider its prior actions stems from 49 U. S. C. § 10327(g), which provides:
“The Commission may, at any time on its own initiative because of material error, new evidence, or substantially changed circumstances—
“(A) reopen a proceeding;
“(B) grant rehearing, reargument, or reconsideration of an action of the Commission; and
“(C) change an action of the Commission.
“An interested party may petition to reopen and reconsider an action of the Commission under this paragraph under regulations of the Commission.”
When the Commission reopens a proceeding for any reason and, after reconsideration, issues a new and final order setting forth the rights and obligations of the parties, that order — even if it merely reaffirms the rights and obligations set forth in the original order — is re viewable on its merits. See, e. g., United States v. Seatrain Lines, Inc., 329 U. S. 424 (1947). Where, however, the Commission refuses to reopen a proceeding, what is reviewable is merely the lawfulness of the refusal. Absent some provision of law requiring a reopening (which is not asserted to exist here), the basis for challenge must be that the refusal to reopen was “arbitrary, capricious, [or] an abuse of discretion.” 5 U. S. C. §706 (2)(A). We have said that overturning the refusal to reopen requires “a showing of the clearest abuse of discretion,” United States v. Pierce Auto Freight Lines, Inc., 327 U. S. 515, 534-535 (1946), and we have actually reversed the ICC only once, see Atchison, T. & S. F. R. Co. v. United States, 284 U. S. 248 (1932), in a decision that was “promptly restricted ... to its special facts, . . . and . . . stands virtually alone.” ICC v. Jersey City, 322 U. S. 503, 515 (1944). See also Bowman Transportation, Inc. v. Arkansas-Best Freight System, Inc., 419 U. S. 281, 295-296 (1974). More importantly for present purposes, all of our cases entertaining review of a refusal to reopen appear to have involved petitions alleging “new evidence” or “changed circumstances” that rendered the agency’s original order inappropriate. See id., at 295, and cases cited therein; Jersey City, supra, at 514-518, and cases cited therein. We know of no case in which we have reviewed the denial of a petition to reopen based upon no more than “material error” in the original agency decision. There is good reason for distinguishing between the two. If review of denial to reopen for new evidence or changed circumstances is unavailable, the petitioner will have been deprived of all opportunity for judicial consideration-even on a “clearest abuse of discretion” basis — of facts which, through no fault of his own, the original proceeding did not contain. By contrast, where no new data but only “material error” has been put forward as the basis for reopening, an appeal places before the courts precisely the same substance that could have been brought there by appeal from the original order — but asks them to review it on the strange, one-step-removed basis of whether the agency decision is not only unlawful, but so unlawful that the refusal to reconsider it is an abuse of discretion. Such an appeal serves no purpose whatever where a petition for reconsideration has been filed within a discretionary review period specifically provided by the agency (and within the period allotted for judicial review of the original order), since in that situation the petition tolls the period for judicial review of the original order, which can therefore be appealed to the courts directly after the petition for reconsideration is denied. And where the petition is filed outside that period (and outside the period for judicial review of the original order) judicial review would serve only the peculiar purpose of extending indefinitely the time within which seriously mistaken agency orders can be judicially overturned. That is to say, the Hobbs Act’s 60-day limitation provision would effectively be subjected to a proviso that reads: “Provided, however, that if the agency error is so egregious that refusal to correct it would be an abuse of discretion, judicial review may be sought at any time.”
For these reasons, we agree with the conclusion reached in an earlier case by the Court of Appeals that, where a party petitions an agency for reconsideration on the ground of “material error,” i. e., on the same record that was before the agency when it rendered its original decision, “an order which merely denies rehearing of. . . [the prior] order is not itself reviewable.” Microwave Communications, Inc. v. FCC, 169 U. S. App. D. C. 154, 156, n. 7, 515 F. 2d 385, 387, n. 7 (1974). See also SEC v. Louisiana Public Service Comm’n, 353 U. S. 368, 371-372 (1957); National Bank of Davis v. Comptroller of Currency, 233 U. S. App. D. C. 284, 285, and n. 3, 725 F. 2d 1390, 1391, and n. 3 (1984); 5 U. S. C. § 701(a)(2). This rule is familiar from other contexts. If a judicial panel or an en banc court denies rehearing, no one supposes that that denial, as opposed to the panel opinion, is an appealable action (though the filing of a timely rehearing petition, like the filing of a timely petition for agency reconsideration, extends the time for appealing from the original decision).
It is irrelevant that the Commission’s order refusing reconsideration discussed the merits of the unions’ claims at length. Where the Commission’s formal disposition is to deny reconsideration, and where it makes no alteration in the underlying order, we will not undertake an inquiry into whether reconsideration “in fact” occurred. In a sense, of course, it always occurs, since one cannot intelligently rule upon a petition to reconsider without reflecting upon, among other things, whether clear error was shown. It would hardly be sensible to say that the Commission can genuinely deny reconsideration only when it gives the matter no thought; nor to say that the character of its action (as grant or denial) depends upon whether it chooses to disclose its reasoning. Rather, it is the Commission’s formal action, rather than its discussion, that is dispositive. Accordingly, the petitions for review of the Commission’s October 25, 1983, order refusing to reconsider its May 18, 1983, refusal to clarify should have been dismissed.
That portion of the concurrence which deals with the issue of jurisdiction (Part I) consists largely of the citation and discussion of numerous cases affording judicial review of agency refusals to reopen. In the third from last paragraph, however, one finds the acknowledgment that all these cases involved refusals “based upon new evidence or changed circumstances” rather than upon “material error,” post, at 293-294, and are therefore fully in accord with the principle set forth in the present opinion. The only point of dispute between this opinion and the concurrence is whether separate treatment of refusals to reopen based on material error has some basis in statute or is rather, as the concurrence would have it, “a pure creature of judicial invention.” Post, at 294.
Even if our search for statutory authorization were limited to the text of the Hobbs Act, it seems to us not inventiveness but the most plebeian statutory construction to find implicit in the 60-day limit upon judicial review a prohibition against the agency’s permitting, or a litigant’s achieving, perpetual availability of review by the mere device of filing a suggestion that the agency has made a mistake and should consider the matter again. Substantial disregard of the Hobbs Act is effected, not by our opinion, but by what the concurrence delivers (after having rejected our views) in Part II of its opinion: on-the-merits review of an agency decision of law rendered 14 months before the petition for review was filed, using the same standard of review that would have been applied had appeal been filed within the congressionally prescribed 60-day period.
Statutory authority for preventing this untoward result need not be sought solely in the Hobbs Act, however. While the Hobbs Act specifies the form of proceeding for judicial review of ICC orders, see 5 U. S. C. § 703, it is the Administrative Procedure Act (APA) that codifies the nature and attributes of judicial review, including the traditional principle of its unavailability “to the extent that. . . agency action is committed to agency discretion by law.” 5 U. S. C. §701 (a)(2). We have recently had occasion to apply this limitation to the general grant of jurisdiction contained in 28 U. S. C. § 1331, see Heckler v. Chaney, 470 U. S. 821 (1985); it applies to the general grant of jurisdiction of the Hobbs Act as well. In Chaney we found that the type of agency decision in question “has traditionally been ‘committed to agency discretion,’ and . . . that the Congress enacting the APA did not intend to alter that tradition.” Id., at 832. As discussed above, we perceive that a similar tradition of non-reviewability exists with regard to refusals to reconsider for material error, by agencies as by lower courts; and we believe that to be another tradition that 5 U. S. C. § 701(a)(2) was meant to preserve. We are confirmed in that view by the impossibility of devising an adequate standard of review for such agency action. One is driven either to apply the ordinary standards for reviewing errors of fact or law (in which event the time limitation of the Hobbs Act — or whatever other time limitation applies to the particular case — will be entirely frustrated); or else to adopt some “clearly erroneous” standard (which produces the strange result that only really bad mistakes escape the time limitation — whatever “really bad” might mean in this context where great deference is already accorded to agency action). The concurrence chooses to impale itself upon the first horn of this dilemma.
The concurrence’s effort to bring SEC v. Chenery Corp., 332 U. S. 194 (1947), into the present discussion is misguided. That case pertains to the basis that a court may use for the affirmance of agency action that is reviewable. (It may not affirm on a basis containing any element of discretion-including discretion to find facts and interpret statutory ambiguities — that is not the basis the agency used, since that would remove the discretionary judgment from the agency to the court.) Chenery has nothing whatever to do with whether agency action is reviewable. It does not establish, as the concurrence evidently believes, the principle that if the agency gives a “reviewable” reason for otherwise unreviewable action, the action becomes reviewable. To demonstrate the falsity of that proposition it is enough to observe that a common reason for failure to prosecute an alleged criminal violation is the prosecutor’s belief (sometimes publicly stated) that the law will not sustain a conviction. That is surely an eminently “reviewable” proposition, in the sense that courts are well qualified to consider the point; yet it is entirely clear that the refusal to prosecute cannot be the subject of judicial review.
Finally, we may note that the concurrence’s solution to review of denials of reconsideration, in addition to nullifying limitation periods, is simply not workable (or not workable on any basis the concurrence has explained) in the vast majority of cases. The concurrence reviews the Commission’s stated conclusions regarding 49 U. S. C. § 11341 on the usual basis applicable to agency conclusions of law, and reviews the Commission’s stated refusal to consider the newly raised (though previously available) issue of RLA crewing rights on an “abuse of discretion” standard. The vast majority of denials of reconsideration, however, are made without statement of reasons, since 5 U. S. C. § 555(e) exempts from the normal APA requirement of “a brief statement of the grounds for denial” agency action that consists of “affirming a prior denial.” One wonders how, in this more normal context, the concurrence would go about determining what answer Chenery supplies to the question of reviewability — and, if the answer permits review, what standard to apply. Under the proper analysis, the solution is clear: If the petition that was denied sought reopening on the basis of new evidence or changed circumstances review is available and abuse of discretion is the standard; otherwise, the agency’s refusal to go back over ploughed ground is nonreviewable.
rH HH
There remains BLE’s appeal from the May 18, 1983, order denying its petition for clarification. While the petition for review was filed more than 60 days after that order was served, we conclude that it was nonetheless effective, because the timely petition for administrative reconsideration stayed the running of the Hobbs Act’s limitation period until the petition had been acted upon by the Commission. A contrary conclusion is admittedly suggested by the language of the Hobbs Act and of 49 U. S. C. §10327(i), which provides that, “Notwithstanding” the provision authorizing the Commission to reopen and reconsider its orders (§ 10327(g)), “an action of the Commission ... is final on the date on which it is served, and a civil action to enforce, enjoin, suspend, or set aside the action may be filed after that date.” This would seem to mean that the pendency of reconsideration motions does not render Commission orders nonfinal for purposes of triggering the Hobbs Act limitations period. The same argument could be made, however, with respect to a similar provision of the APA, 5 U. S. C. §704, which reads in relevant part: “Except as otherwise expressly required by statute, agency action otherwise final is final for the purposes of this section [entitled ‘Actions Reviewable’] whether or not there has been presented or determined an application for . . . any form of reconsider-ations, or, unless the agency otherwise requires by rule and provides that the action meanwhile is inoperative, for an appeal to superior agency authority.” That language has long been construed by this and other courts merely to relieve parties from the requirement of petitioning for rehearing before seeking judicial review (unless, of course, specifically required to do so by statute — see, e. g., 15 U. S. C. §§717r, 3416(a)), but not to prevent petitions for reconsideration that are actually filed from rendering the orders under reconsideration nonfinal. See American Farm Lines v. Black Ball Freight Service, 397 U. S. 532, 541 (1970) (dictum); CAB v. Delta Air Lines, Inc., 367 U. S. 316, 326-327 (1961) (dictum); id., at 339-343 (Whittaker, J., dissenting); Outland v. CAB, 109 U. S. App. D. C. 90, 93, 284 F. 2d 224, 227 (1960). We can find no basis for distinguishing the language of § 10327(f) from that of § 704. The appeal from the denial of clarification was therefore timely.
As with the Commission’s denial of reconsideration, however, its denial of clarification was not an appealable order. If BLE’s motion is treated as a genuine “Petition for Clarification” — ! e., as seeking nothing more than specification, one way or the other, of what the original order meant with regard to crewing rights — then the denial is unappealable because BLE was not “aggrieved” by it within the meaning of the Hobbs Act. BLE could have been aggrieved by a refusal to clarify in this narrow sense only if the refusal left it uncertain as to the Commission’s view of its rights or obligations, which plainly was not the case. Though the May 18, 1983, order denied the petition for clarification, the text of the denial made it unmistakably clear that the Commission interpreted the October 20, 1982, order as authorizing MKT and DRGW to use their own crews. BLE could, of course, disagree with that construction, but it could hardly complain that the clarification it sought had not been provided.
In fact, however, we think that BLE’s petition was understood by all of the parties to be in effect a petition to reopen. BLE did not merely ask the Commission for clarification; it asked for clarification “in the manner set forth [in the petition],” App. in Nos. 83-2290 and 83-2317 (CADC), p. 5, %. e., for “clarification” that the October 20, 1982, order meant what the unions believed it to mean. Most precisely described, the petition sought, in the alternative, clarification or (in the event clarification would be contrary to the union’s interpretation) reopening of the earlier order. Even when the petition is viewed as a petition to reopen, however, the Commission’s denial is no more reviewable than is its denial of the petitions for reconsideration discussed earlier. BLE brought forth no new evidence or changed circumstances; it merely urged the Commission to correct what BLE thought to be a serious error of law. That should have been sought many months earlier, by an appeal from the original order.
We are not prepared to acknowledge an exception to that requirement where an order is ambiguous, so that a party might think that its interests are not infringed. The remedy for such ambiguity is to petition the Commission for reconsideration within the 60-day period, enabling judicial review to be pursued (if Commission resolution of the ambiguity is adverse) after disposition of that petition. Otherwise, the time limits of the Hobbs Act would be held hostage to ever-present ambiguities. If, of course, the ICC’s action here had gone beyond what was (at most) clarification of an ambiguity, and in the guise of interpreting the original order in fact revised it, that would have been a new order immediately ap-pealable. It is impossible to make such a contention here. It was, at the very most, arguable that the Commission’s routine reference to the general NW-BN-Mendocino conditions was meant to cause those conditions to supersede, in the event of conflict, the specific terms of the trackage rights applications that the Commission generally approved — and also far from certain that any conflict between the two existed, since it was unclear whether the protective conditions extended to the situation in which the landlord and tenant railroads conduct no joint operations and the tenant carries only traffic for its own account.
The case is remanded to the Court of Appeals with instructions to dismiss the petitions for lack of jurisdiction.
Vacated and remanded.
Ordinarily, a petition for relief from a final order is denominated a “petition to reopen.” See 49 CFR §§ 1115.3(a), 1115.4 (1986). A Commission rule, however, permits parties to “see[k] relief not provided for in any other rule,” 49 CFR § 1117.1 (1986), including clarification of the terms of a prior order. See Burlington Northern Inc. v. United States, 459 U. S. 131, 136 (1982).
The ICC’s regulations, for example, provide as follows:
“(a) A discretionary appeal is permitted. It will be designated a ‘petition for administrative review,’ except that, when it is related to an action of the entire Commission in the first instance, it must be designated a ‘petition to reopen.’
“(b) The petition will be granted only upon a showing of one or more of the following points:
“(3) The prior action was taken by the entire Commission in the first instance, and involves material error.
“(e) Petitions must be filed within 20 days after the service of the action or within any further period (not to exceed 20 days) as a division or the Commission may authorize.” 49 CFR § 1115.3 (1986).