Mr. Justice Rehnquist
delivered the opinion of the Court.
The Clean Air Act authorizes the Administrator of the Environmental Protection Agency to promulgate “emission standards” for hazardous air pollutants “at the level which in his judgment provides an ample margin of safety to protect the public health.” § 112 (b)(1)(B), 84 Stat. 1685, 42 U. S. C. § 1857c-7 (b)(1)(B). The emission of an air pollutant in violation of an applicable emission standard is prohibited by § 112 (c)(1)(B) of the Act, 42 U. S. C. § 1857c-7 (c)(1)(B). The knowing violation of the latter section, in turn, subjects the violator to fine and imprisonment under the provisions of § 113 (c)(1)(C) of the Act, 42 U. S. C. § 1857c^8 (c)(1)(C) (1970 ed., Supp. V). The final piece in this statutory puzzle is § 307 (b) of the Act, 84 Stat. 1708, 42 U. S. C. § 1857h-5(b) (1970 ed., Supp. V), which provides in pertinent part:
‘ “(1) A petition for review of action of the Administrator in promulgating . . . any emission standard under section 112 .. . may be filed only in the United States Court of Appeals for the District of Columbia. . . . Any such petition shall be filed within 30 days from the date of such promulgation or approval, or after such date if such petition is based solely on grounds arising after such 30th day.
“(2) Action of the Administrator with respect to which review could have been obtained under paragraph (1) shall not be subject to judicial review in civil or criminal proceedings for enforcement.”
It is within this legislative matrix that the present criminal prosecution arose:
Petitioner was indicted in the United States District Court for the Eastern District of Michigan for violation of § 112 (c)(1)(B). The indictment alleged that petitioner, while engaged in the demolition of a building in Detroit, failed to comply with 40 CFR § 61.22 (d) (2) (i) (1975). That regulation, described in its caption as a “National Emission Standard for Asbestos,” specifies procedures to be followed in connection with building demolitions, but does not by its terms limit emissions of asbestos which occur during the course of a demolition. The District Court granted petitioner’s motion to dismiss the indictment on the ground that no violation of § 112 (c) (1) (B), necessary to establish criminal liability under §113 (c)(1)(C), had been alleged, because the cited regulation was not an “emission standard” within the meaning of § 112 (c). The United States Court of Appeals for the Sixth Circuit reversed, 545 F. 2d 1 (1976), holding that Congress had in § 307 (b) precluded petitioner from questioning in a criminal proceeding whether a regulation ostensibly promulgated under § 112 (b)(1)(B) was in fact an emission standard. We granted certiorari, 430 U. S. 953 (1977), and we now reverse.
I
We do not intend to make light of a difficult question of statutory interpretation when we say that the basic question in this case may be phrased: “When is an emission standard not an emission standard?” Petitioner contends, and the District Court agreed, that while the preclusion and exclusivity provisions of § 307 (b) of the Act prevented his obtaining “judicial review” of an emission standard in this criminal proceeding, he was nonetheless entitled to claim that the administrative regulation cited in the indictment was actually not an emission standard at all. The Court of Appeals took the contrary view. It held that a regulation designated by the Administrator as an “emission standard,” however different in content it might be from what Congress had contemplated when it authorized the promulgation of emission standards, was sufficient to support a criminal charge based upon § 112 (c), unless it had been set aside in an appropriate proceeding commenced in the United States Court of Appeals for the District of Columbia Circuit pursuant to § 307 (b).
The Court of Appeals in its opinion relied heavily on Yakus v. United States, 321 U. S. 414 (1944), in which this Court held that Congress in the context of criminal proceedings could require that the validity of regulatory action be challenged in a particular court at a particular time, or not at all. That case, however, does not decide this one. Because § 307 (b) expressly applies only to “emission standards,” we must still inquire as to the validity of the Government’s underlying assumption that the Administrator’s mere designation of a regulation as an “emission standard” is sufficient to foreclose any further inquiry in a criminal prosecution under § 113 (c) (1) (C) of the Act. For the reasons hereafter stated, we hold that one such as respondent who is charged with a criminal violation under the Act may defend on the ground that the “emission standard” which he is charged with having violated was not an “emission standard” within the contemplation of Congress when it employed that term, even though the “emission standard” in question has not been previously reviewed under the provisions of § 307 (b) of the Act.
II
In resolving this question, we think the statutory provisions of the Clean Air Act are far less favorable to the Government’s position than were the provisions of the Emergency Price Control Act considered in Yakus. The broad language of that statute gave clear evidence of congressional intent that any actions taken by the Price Administrator under the purported authority of the designated sections of. the Act should be challenged only in the Emergency Court of Appeals. Nothing has been called to our attention which would lead us to disagree with the Government’s description of the judicial review provisions of that Act:
“Review of price control regulations was centralized in the Emergency Court of Appeals under a statute giving that court ‘exclusive’ jurisdiction of all non-constitutional challenges to price control regulations. The Court had no difficulty construing the statute as precluding any attack on a regulation in a criminal case (321 U. S., at 430-431), even though the statute did not explicitly mention criminal cases.” Brief for United States 18.
This relatively simple statutory scheme contrasts with the Clean Air Act’s far more complex interrelationship between the imposition of criminal sanctions and judicial review of the Administrator’s actions. The statutory basis for imposition of criminal liability under subchapter I of the Act, under which this indictment was brought, is § 113 (c)(1), 84 Stat. 1687, as amended, 42 U. S. C. § 1857c-8 (c)(1) (1970 ed. and Supp. V):
“(c)(1) Any person who knowingly—
“(A) violates any requirement of an applicable implementation plan (i) during any period of Federally assumed enforcement, or (ii) more than 30 days after having been notified by the Administrator under subsection (a)(1) that such person is violating such requirement, or
“(B) violates or fails or refuses to comply with any order issued by the Administrator under subsection (a), or
“(C) violates section 111 (e), section 112 (c), or section 119 (g)
“shall be punished by a fine of not more than $25,000 per day of violation, or by imprisonment for not more than one year, or by both. If the conviction is for a violation committed after the first conviction of such person under this paragraph, punishment shall be by a fine of not more than $50,000 per day of violation, or by imprisonment for not more than two years, or by both.”
Each of the three separate subsections in the quoted language creates criminal offenses. The first of them, subsection (A), deals with violations of applicable implementation plans after receipt of notice of such violation. Under § 307 (b) (1), judicial review of the Administrator’s action in approving or promulgating an implementation plan is not restricted to the Court of Appeals for the District of Columbia Circuit, but may be had “in the United States Court of Appeals for the appropriate circuit.” But § 307 (b) (2) does provide that the validity of such plans may not be reviewed in the criminal proceeding itself.
Subsection (C), which we discuss before turning to subsection (B), provides criminal penalties for violations of three separate sections of the Act: § 111 (e), 84 Stat. 1684, 42 U. S. C. § 1857c-6 (e), which prohibits operation of new stationary sources in violation of “standards of performance” promulgated by the Administrator; § 112 (c), which is the offense charged in this case; and § 119 (g), 88 Stat. 254, 42 U. S. C. § 1857c-10 (g) (1970 ed., Supp. V), which requires compliance with an assortment of administrative requirements, set out in more detail below. The Administrator’s actions in promulgating “standards of performance” under § 111, or “emission standards” under § 112 are, by the provisions of § 307 (b)(1), made reviewable exclusively in the Court of Appeals for the District of Columbia Circuit. However, his actions under subsections (A), (B), and (C) of § 119 (c)(2), compliance with which is required by § 119 (g)(2), are reviewable “in the United States Court of Appeals for the appropriate circuit.” Those subsections define the Administrator’s authority to issue compliance date extensions to particular stationary sources with regard to various air pollution requirements. The preclusive provisions of § 307 (b) (2) prohibit challenges to all of these administrative actions in both civil and criminal enforcement proceedings. But these restrictive review provisions do not apply to other violations of § 119 (g); with regard to those offenses, the invalidity of administrative action may be raised as a defense to the extent allowable in the absence of such restrictions.
Finally, subsection (B) of § 113 (c)(1) subjects to criminal penalties “any person who knowingly . . . violates or fails or refuses to comply with any order issued by the Administrator under subsection (a).” Subsection (a), in turn, empowers the Administrator to issue orders requiring compliance, not only with those regulations for which criminal penalties are provided under subsections (A) and (C), but also with the record-keeping and inspection requirements of § 114, 42 U. S. C. § 1857c-9 (1970 ed., Supp. V), for which only civil penalties are ordinarily available under § 113 (b)(4). The restrictive review provisions of § 307 (b)(1), again do not apply to orders issued under § 113 (a) or to the underlying requirements of § 114. Those administrative actions would likely be reviewable under the Administrative Procedure Act, 5 U. S. C. § 701 et seg., and any infirmity in them could be raised as a defense in enforcement proceedings to the same extent as it could be in the absence of a provision such as § 307 (b)(2).
Ill
The conclusion we draw from this excursion into the complexities of the criminal sanctions provided by the Act are several. First, Congress has not chosen to prescribe either civil or criminal sanctions for violations of every rule, regulation, or order issued by the Administrator. Second, Congress, as might be expected, has imposed civil liability for a wider range of violations of the orders of the Administrator than those for which it has imposed criminal liability. Third, even where Congress has imposed criminal liability for the violation of an order of the Administrator, it has not uniformly precluded judicial challenge to the order as a defense in the criminal proceeding. Fourth, although Congress has applied the preclusion provisions of § 307 (b) (2) to implementation plans approved by the Administrator, and it has in § 113 (c)(1)(A) provided criminal penalties for violations of those plans, it has nonetheless required, under normal circumstances, that a violation continue for a period of 30 days after receipt of notice of the violation from the Administrator before the criminal sanction may be imposed.
These conclusions in no way detract from the fact that Congress has precluded judicial review of an “emission standard” in the court in which the criminal proceeding for the violation of the standard is brought. Indeed, the- conclusions heighten the importance of determining what it was that Congress meant by an “emission standard,” since a violation of that standard is subject to the most stringent criminal liability-imposed by § 113 (c) (1) of the Act: Not only is the Administrator’s promulgation of the standard not subject to judicial review in the criminal proceeding, but no prior notice of violation from the Administrator is required as a condition for criminal liability. Since Congress chose to attach these stringent sanctions to the violation of an emission standard, in contrast to the violation of various other kinds of orders that might be issued by the Administrator, it is crucial to determine whether the Administrator’s mere designation of a regulation as an “emission standard” is conclusive as to its character.
The stringency of the penalty imposed by Congress lends substance to petitioner’s contention that Congress envisioned a particular type of regulation when it spoke of an “emission standard.” The fact that Congress dealt moré leniently, either in terms of liability, of notice, or of available defenses, with other infractions of the Administrator’s orders suggests that it attached a peculiar importance to compliance with “emission standards.” Unlike the situation in Yakus, Congress in the Clean Air Act singled out violators of this generic form of regulation, imposed criminal penalties upon them which would not be imposed upon violators of other orders of the Administrator, and precluded them from asserting defenses which might be asserted by violators of other orders of the Administrator. All of this leads us to conclude that Congress intended, within broad limits, that “emission standards” be regulations of a certain type, and that it did not empower the Administrator, after the manner of Humpty Dumpty in Through the Looking-Glass, to make a regulation an “emission standard” by his mere designation.
The statutory scheme supports the conclusion that § 307 (b)(2), in precluding judicial review of the validity of emission standards, does not relieve the Government of the duty of proving, in a prosecution under § 113 (c)(1)(C), that the regulation allegedly violated is an emission standard. Here, the District Qourt properly undertook to resolve that issue. In so doing, the court did not undermine the twin congressional purposes of insuring that the substantive provisions of the standard would be uniformly applied and interpreted and that the circumstances of its adoption would be quickly reviewed by a single court intimately familiar with administrative procedures. The District Court did not presume to judge the wisdom of the regulation or to consider the adequacy of the procedures which led to its promulgation, but merely concluded that it was not an emission standard.
In sum, a survey of the totality of the statutory scheme does not compel agreement with the Government’s contention that Congress intended that the Administrator’s designation of a regulation as an emission standard should be conclusive in a criminal prosecution. At the very least, it may be said that the issue is subject to some doubt. Under these circumstances, we adhere to .the familiar rule that, “where there is ambiguity in a criminal statute, doubts are resolved in favor of the defendant.” United States v. Bass, 404 U. S. 336, 348 (1971). Cf. Rewis v. United States, 401 U. S. 808, 812 (1971).
We conclude, therefore, that a federal court in which a criminal prosecution under § 113 (c)(1)(C) of the Clean Air Act is brought may determine whether or not the regulation which the defendant is alleged to have violated is an “emission standard” within the meaning of the Act. We are aware of the possible dangers that flow from this interpretation; district courts will be importuned, under the guise of making a determination as to whether a regulation is an “emission standard,” to engage in judicial review in a manner that is precluded by § 307 (b) (2) of the Act. This they may not do. The narrow inquiry to be addressed by the court in a criminal prosecution is not whether the Administrator has complied with appropriate procedures in promulgating the regulation in question, or whether the particular regulation is arbitrary, capricious, or supported by the administrative record. Nor is the court to pursue any of the other familiar inquiries which arise in the course of an administrative review proceeding. The question is only whether the regulation which the defendant is alleged to have violated is on its'face an “emission standard” within the broad limits of the congressional meaning of that term.
IV
It remains to be seen whether the District Court reached the correct conclusion with regard to the regulation here in question. In the Act, Congress has given a substantial indication of the intended meaning of the term “emission standard.” Section 112 on its face distinguishes between emission standards and the techniques to be utilized in achieving those standards. Under § 112 (c) (1) (B) (ii), the Administrator is empowered temporarily to exempt certain facilities from the burden of compliance with an emission standard, “if he finds that such period is necessary for the installation of controls.” In specified circumstances, the President, under § 112 (c) (2), has the same power, “if he finds that the technology to implement such standards is not available.” Section 112 (b) (2) authorizes the Administrator to issue information on “pollution control techniques.”
Most clearly supportive of petitioner’s position that a standard was intended to be a quantitative limit on emissions is this provision of §112 (b)(1)(B): “The Administrator shall establish any such standard at the level which in his judgment provides an ample margin of safety to protect the public health from such hazardous air pollutant.” (Emphasis added.) All these provisions lend force to the conclusion that a standard is a quantitative “level” to be attained by use of “techniques,” “controls,” and “technology.” This conclusion is fortified by recent amendments to the Act, by which Congress authorized the Administrator to promulgate a “design, equipment, work practice, or operational standard” when “it is not feasible to prescribe or enforce an emission standard.” Clean Air Act Amendments of 1977, Pub. L. 95-95, § 110, 91 Stat. 703.
This distinction, now endorsed by Congress, between “work practice standards” and “emission standards” first appears in the Administrator’s own account of the development of this regulation. Although the Administrator has contended that a “work practice standard” is just another type of emission standard, the history of this regulation demonstrates that he chose to regulate work practices only when it became clear he could not regulate emissions. The regulation as originally proposed would have prohibited all visible emissions of asbestos during the course of demolitions. 36 Fed. Reg. 23242 (1971). In adopting the final form of the regulation, the Administrator concluded “that the no visible emission requirement would prohibit repair or demolition in many situations, since it would be impracticable, if not impossible, to do such work without creating visible emissions.” 38 Fed. Reg. 8821 (1973). Therefore the Administrator chose to “specif [y] certain work practices” instead. Ibid.
The Government concedes that, prior to the 1977 Amendments, the statute was ambiguous with regard to whether a work-practice standard was properly classified as an emission standard, but argues that this Court should defer to the Administrator’s construction of the Act: Brief for United States 32, and n. 22. While such deference is entirely appropriate under ordinary circumstances, in this case the 1977 Amendments to the Clean Air Act tend to undercut the administrative construction. The Senate Report reiterated its “strong preference for numerical emission limitations/’ but endorsed the addition of § 112 (e) to the Act to allow the use of work-practice standards “in a very few limited cases.” S. Rep. No. 95-127, p. 44 (1977). Although the Committee agreed that the Amendments would authorize the regulation involved here, it refrained from endorsing the Administrator’s view that the regulation had previously been authorized as an emission standard under § 112 (c). The clear distinction drawn in § 112 (e) between work-practice standards and emission standards practically forecloses any such inference. Cf. Red Lion Broadcasting Co. v. FCC, 395 U. S. 367, 380-381 (1969).
For all of the foregoing reasons, we conclude that the work-practice standard involved here was not an emission standard. The District Court’s order dismissing the indictment was therefore proper, and the judgment of the Court of Appeals is
Reversed.
Section 119, which was in effect at the inception of this prosecution, has lately been replaced by a new § 113 (d). Clean Air Act Amendments of 1977, Pub. L. 95-95, § 112, 91 Stat. 705.
The severity of the scheme is accentuated by the fact that persons subject to the Act, including innumerable small businesses, may protect themselves against arbitrary administrative action only by daily perusal of proposed emission standards in the Federal Register and by immediate initiation of litigation in the District of Columbia to protect their interests.
Such a preliminary analysis of administrative action is hardly unique. Only last Term, in E. I. du Pont de Nemours & Co. v. Train, 430 U. S. 112 (1977), this Court approved such an initial examination of regulations promulgated under the Federal Water Pollution Control Act. As we. described the issue presented there:
“If EPA is correct that its regulations are ‘effluent limitation[s] under section 301,’ the regulations are directly reviewable in the Court of Appeals. If industry is correct that the regulations can only be considered § 304 guidelines, suit to review the regulations could probably be brought only in the District Court, if anywhere. Thus, the issue of jurisdiction to review the regulations is intertwined with the issue of EPA’s power to issue the regulations.” Id., at 124-125.
In that case, the District Court had conducted a careful analysis, concluding that the regulations in question were “effluent limitations,” 383 F. Supp. 1244 (WD Va. 1974), aff’d, 528 F. 2d 1136 (CA4 1975), just as the District Court here concluded that this regulation is not an emission standard.
Since oral argument, Congress has again confirmed that the term "emission standard” is not broad enough to include a work-practice standard. Congress has amended §307 (b)(1), which originally governed review of "any emission standard under section 112,” to cover “any emission standard or requirement under section 112.” Pub. L. No. 95-190, § 14 (a) (79), 91 Stat. 1404. As Mr. Justice Stevens’ dissent notes, post, at 306, Congress has yet to apply this recognition to the enforcement provisions of § 112 (c).
Our Brother SteveNS quite correctly points out, post, at 302, that an administrative “ 'contemporaneous construction’ ” of a statute is entitled to considerable weight, and it is true that the originally proposed regulations contain, with respect to some uses of asbestos, the sort of provisions which the Administrator and the Congress later designated as “work practice standards.” It bears noting, however, that these regulations can only be said to define by implication the meaning of the term “emission standard.” The Administrator promulgated both of them; both were denominated “emission standards”; and it is undoubtedly a fair inference that the Administrator thought each to be an “emission standard.” But neither the regulations themselves nor the comments accompanying them give any indication of the Administrator’s reasons for concluding that Congress, in authorizing him to promulgate “emission standards,” intended to include “work practice standards” within the meaning of that term. See 38 Fed. Reg. 8820-8822, 8829-8830 (1973); 36 Fed. Reg. 23239-23240, 23242 (1971).
This lack of specific attention to the statutory authorization is especially important in light of this Court’s pronouncement in Skidmore v. Swift & Co., 323 U. S. 134, 140 (1944), that one factor to be considered in giving weight to an administrative ruling is “the thoroughness evident in its consideration, the validity of its reasoning, its consistency with earlier and later pronouncements, and all those factors which give it power to persuade, if lacking power to control.” The Administrator’s remarks with regard to these regulations clearly demonstrate that he carefully considered available techniques and methods for controlling asbestos emissions, but they give no indication of “the validity of [his] reasoning” in concluding that he was authorized to promulgate these techniques as an “emission standard,” within the statutory definition. Since this Court can only speculate as to his reasons for reaching that conclusion, the mere promulgation of a regulation, without a concomitant exegesis of the statutory authority for doing so, obviously lacks “power to persuade” as to the existence of such authority.
By contrast, the Wage and Hour Administrator in Gemsco, Inc. v. Walling, 324 U. S. 244 (1945), referred to in Brother Stevens’ dissenting opinion, post, at 299-300, n. 16, gave clear indication of his reasons for concluding that the administrative regulation prohibiting industrial homework was authorized by § 8 (f) of the Fair Labor Standards Act, 52 Stat. 1065. The statute empowered the Administrator to issue orders necessary “to prevent the circumvention or evasion” of orders issued un,der § 8 (f), and the Administrator specifically found that the practice prohibited by the order there challenged “ Turnishe[d] a ready means of circumventing or evading the minimum wage order for this Industry.’ ” 324 U. S., at 250, n. 9. In this case, the Administrator of the Environmental Protection Agency offered no comparable analysis of his statutory authority.
In Train v. Natural Resources Defense Council, 421 U. S. 60 (1975), relied upon by Brother Stevens’ dissent, this Court was not persuaded by “a single sentence in the Federal Register,” post, at 301 n. 18, but by our own “analysis of the structure and legislative history of the Clean Air Amendments,” 421 U. S., at 86, which led us to a result consistent with the Administrator’s prior practice. Here, our analysis mandates a contrary conclusion, which is not undercut by the Administrator’s unexplained exercise of supposed authority.
Finally, as noted in n. 4, supra, Congress has not explicitly adopted the Administrator’s present position with regard to the meaning of the term “emission standard,” although it could easily have done so. It is true, as that dissent remarks, post, at 305-306, n. 24, that Congress has responded to concerns expressed by the Administrator. However, he first advised us of the deficiency in § 307 (b) at oral argument, and even then did not suggest that under the statutory scheme as it presently exists his work-practice standards may be unenforceable. This piecemeal approach to the complexities of the Act hardly displays the “thoroughness . . . in . . . consideration/’ Skidmore, supra, at 140, which we would expect to find in an administrative construction.