delivered the opinion of the Court.
The appellees were charged by information with violation of the Federal Regulation of Lobbying Act, 60 Stat. 812, 839, 2 U. S. C. §§ 261-270. Relying on its previous *614decision in National Association of Manufacturers v. McGrath, 103 F. Supp. 510, vacated as moot, 344 U. S. 804, the District Court dismissed the information on the ground that the Act is unconstitutional. 109 F. Supp. 641. The case is here on direct appeal under the Criminal Appeals Act, 18 U. S. C. § 3731.
Seven counts of the information are laid under § 305, which requires designated reports to Congress from every person “receiving any contributions or expending any money” for the purpose of influencing the passage or defeat of any legislation by Congress.1 One such count charges the National Farm Committee, a Texas corpora*615tion, with failure to report the solicitation and receipt of contributions to influence the passage of legislation which would cause a rise in the price of agricultural commodities and commodity futures and the defeat of legislation which would cause a decline in those prices. The remaining six counts under § 305 charge defendants Moore and Harriss with failure to report expenditures having the same single purpose. Some of the alleged expenditures consist of the payment of compensation to others to communicate face-to-face with members of Congress, at public functions and committee hearings, concerning legislation affecting agricultural prices; the other alleged expenditures relate largely to the costs of a campaign to induce various interested groups and individuals to communicate by letter with members of Congress on such legislation.
The other two counts in the information are laid under § 308, which requires any person “who shall engage himself for pay or for any consideration for the purpose of attempting to influence the passage or defeat of any legislation” to register with Congress and to make specified disclosures.2 These two counts allege in considerable *616detail that defendants Moore and Linder were hired to express certain views to Congress as to agricultural prices or to cause others to do so, for the purpose of attempting to influence the passage of legislation which would cause a rise in the price of agricultural commodities and commodity futures and a defeat of legislation which would cause a decline in such prices; and that pursuant to this undertaking, without having registered as required by *617§ 308, they arranged to have members of Congress contacted on behalf of these views, either directly by their own emissaries or through an artificially stimulated letter campaign.3
We are not concerned here with the sufficiency of the information as a criminal pleading. Our review under the Criminal Appeals Act is limited to a decision on the alleged “invalidity” of the statute on which the information is based.4 In making this decision, we judge the statute on its face. See United States v. Petrillo, 332 U. S. 1, 6, 12. The “invalidity” of the Lobbying Act is asserted on three grounds: (1) that §§ 305, 307, and 308 are too vague and indefinite to meet the requirements of due process; (2) that §§ 305 and 308 violate the First Amendment guarantees of freedom of speech, freedom of the press, and the right to petition the Government; (3) that the penalty provision of § 310 (b) violates the right of the people under the First Amendment to petition the Government.
I.
The constitutional requirement of definiteness is violated by a criminal statute that fails to give a person of ordinary intelligence fair notice that his contemplated conduct is forbidden by the statute. The underlying principle is that no man shall be held criminally responsible for conduct which he could not reasonably understand to be proscribed.5
*618On the other hand, if the general class of offenses to which the statute is directed is plainly within its terms, the statute will not be struck down as vague, even though marginal cases could be put where doubts might arise. United States v. Petrillo, 332 U. S. 1, 7. Cf. Jordan v. De George, 341 U. S. 223, 231. And if this general class of offenses can be made constitutionally definite by a reasonable construction of the statute, this Court is under a duty to give the statute that construction. This was the course adopted in Screws v. United States, 325 U. S. 91, upholding the definiteness of the Civil Rights Act.6
The same course is appropriate here. The key section of the Lobbying Act is § 307, entitled “Persons to Whom Applicable.” Section 307 provides:
“The provisions of this title shall apply to any person (except a political committee as defined in *619the Federal Corrupt Practices Act, and duly organized State or local committees of a political party), who by himself, or through any agent or employee or other persons in any manner whatsoever, directly or indirectly, solicits, collects, or receives money or any other thing of value to be used principally to aid, or the principal purpose of which person is to aid, in the accomplishment of any of the following purposes:
“(a) The passage or defeat of any legislation by the Congress of the United States.
“(b) To influence, directly or indirectly, the passage or defeat of any legislation by the Congress of the United States.”
This section modifies the substantive provisions of the Act, including § 305 and § 308. In other words, unless a “person” falls within the category established by § 307, the disclosure requirements of § 305 and § 308 are inapplicable.7 Thus coverage under the Act is limited to those persons (except for the specified political committees) who solicit, collect, or receive contributions of money or other thing of value, and then only if “the principal purpose” of either the persons or the contributions is to aid in the accomplishment of the aims set forth in § 307 (a) and (b). In any event, the solicitation, collection, or receipt of money or other thing of value is a prerequisite to coverage under the Act.
The Government urges a much broader construction— namely, that under § 305 a person must report his expenditures to influence legislation even though he does not solicit, collect, or receive contributions as provided in *620§ 307.8 Such a construction, we believe, would do violence to the title and language of § 307 as well as its legislative history.9 If the construction urged by the Government is to become law, that is for Congress to accomplish by further legislation.
We now turn to the alleged vagueness of the purposes set forth in § 307 (a) and (b). As in United States v. Rumely, 345 U. S. 41, 47, which involved the interpretation of similar language, we believe this language should be construed to refer only to “lobbying in its commonly accepted sense” — to direct communication with members of Congress on pending or proposed federal legislation. The legislative history of the Act makes clear that, at the very least, Congress sought disclosure of such direct pressures, exerted by the lobbyists themselves or through their hirelings or through an artificially stimulated letter campaign.10 It is likewise clear that Congress would have *621intended the Act to operate on this narrower basis, even if a broader application to organizations seeking to propagandize the general public were not permissible.11
There remains for our consideration the meaning of “the principal purpose” and “to be used principally to *622aid.” The legislative history of the Act indicates that the term “principal” was adopted merely to exclude from the scope of § 307 those contributions and persons having only an “incidental” purpose of influencing legislation.12 Conversely, the “principal purpose” requirement does not exclude a contribution which in substantial part is to be used to influence legislation through direct communication with Congress or a person whose activities in substantial part are directed to influencing legislation through direct communication with Congress.13 If it were otherwise — if an organization, for example, were exempted *623because lobbying was only one of its main activities— the Act would in large measure be reduced to a mere exhortation against abuse of the legislative process. In construing the Act narrowly to avoid constitutional doubts, we must also avoid a construction that would seriously impair the effectiveness of the Act in coping with the problem it was designed to alleviate.
To summarize, therefore, there are three prerequisites to coverage under §307: (1) the “person” must have solicited, collected, or received contributions; (2) one of the main purposes of such “person,” or one of the main purposes of such contributions, must have been to influence the passage or defeat of legislation by Congress; (3) the intended method of accomplishing this purpose must have been through direct communication with members of Congress. And since § 307 modifies the substantive provisions of the Act, our construction of § 307 will of necessity also narrow the scope of § 305 and § 308, the substantive provisions underlying the information in this case. Thus § 305 is limited to those persons who are covered by § 307; and when so covered, they must report all contributions and expenditures having the purpose of attempting to influence legislation through direct communication with Congress. Similarly, § 308 is limited to those persons (with the stated exceptions14) who are covered by § 307 and who, in addition, engage themselves *624for pay or for any other valuable consideration for the purpose of attempting to influence legislation through direct communication with Congress. Construed in this way, the Lobbying Act meets the constitutional requirement of definiteness.15
*625II.
Thus construed, §§ 305 and 308 also do not violate the freedoms guaranteed by the First Amendment — freedom to speak, publish, and petition the Government.
Present-day legislative complexities are such that individual members of Congress cannot be expected to explore the myriad pressures to which they are regularly subjected. Yet full realization of the American ideal of government by elected representatives depends to no small extent on their ability to properly evaluate such pressures. Otherwise the voice of the people may all too easily be drowned out by the voice of special interest groups seeking favored treatment while masquerading as proponents of the public weal. This is the evil which the Lobbying Act was designed to help prevent.16
Toward that end, Congress has not sought to prohibit these pressures. It has merely provided for a modicum of information from those who for hire attempt to influence legislation or who collect or spend funds for that purpose. It wants only to know who is being hired, who is putting up the money, and how much. It acted in the same spirit and for a similar purpose in passing the Federal Corrupt Practices Act — to maintain the integrity of a basic governmental process. See Burroughs and Cannon v. United States, 290 U. S. 534, 545.
Under these circumstances, we believe that Congress, at least within the bounds of the Act as we have construed it, is not constitutionally forbidden to require the disclosure of lobbying activities. To do so would be to deny Congress in large measure the power of self-protec*626tion. And here Congress has used that power in a manner restricted to its appropriate end. We conclude that §§ 305 and 308, as applied to persons defined in § 307, do not offend the First Amendment.
It is suggested, however, that the Lobbying Act, with respect to persons other than those defined in § 307, may as a practical matter act as a deterrent to their exercise of First Amendment rights. Hypothetical borderline situations are conjured up in which such persons choose to remain silent because of fear of possible prosecution for failure to comply with the Act. Our narrow construction of the Act, precluding as it does reasonable fears, is calculated to avoid such restraint. But, even assuming some such deterrent effect, the restraint is at most an indirect one resulting from self-censorship, comparable in many ways to the restraint resulting from criminal libel laws.17 The hazard of such restraint is too remote to require striking down a statute which on its face is otherwise plainly within the area of congressional power and is designed to safeguard a vital national interest.
III.
The appellees further attack the statute on the ground that the penalty provided in § 310 (b) is unconstitutional. That section provides:
“(b) In addition to the penalties provided for in subsection (a), any person convicted of the misdemeanor specified therein is prohibited, for a period of three years from the date of such conviction, from attempting to influence, directly or indirectly, the passage or defeat of any proposed legislation or from *627appearing before a committee of the Congress in support of or opposition to proposed legislation; and any person who violates any provision of this subsection shall, upon conviction thereof, be guilty of a felony, and shall be punished by a fine of not more than $10,000, or imprisonment for not more than five years, or by both such fine and imprisonment.”
This section, the appellees argue, is a patent violation of the First Amendment guarantees' of freedom of speech and the right to petition the Government.
We find it unnecessary to pass on this contention. Unlike §§ 305, 307, and 308 which we have judged on their face, § 310 (b) has not yet been applied to the appellees, and it will never be so applied if the appellees are found innocent of the charges against them. See United States v. Wurzbach, 280 U. S. 396, 399; United States v. Petrillo, 332 U. S. 1, 9-12.
Moreover, the Act provides for the separability of any provision found invalid.18 If § 310 (b) should ultimately be declared unconstitutional, its elimination would still leave a statute defining specific duties and providing a specific penalty for violation of any such duty. The prohibition of § 310 (b) is expressly stated to be “In addition to the penalties provided for in subsection (a) . . subsection (a) makes a violation of § 305 or § 308 a misdemeanor, punishable by fine or imprisonment or both. Consequently, there would seem to be no obstacle to giving effect to the separability clause as to § 310 (b), if this should ever prove necessary. Compare Electric Bond & Share Co. v. Securities & Exchange Commission, 303 U. S. 419, 433-437.
*628The judgment below is reversed and the cause is remanded to the District Court for further proceedings not inconsistent with this opinion.
Reversed.
Mr. Justice Clark took no part in the consideration or decision of this case.Section 305 provides:
“(a) Every person receiving any contributions or expending any money for the purposes designated in subparagraph (a) or (b) of section 307 shall file with the Clerk between the first and tenth day of each calendar quarter, a statement containing complete as of the day next preceding the date of filing—
“(1) the name and address of each person who has made a contribution of $500 or more not mentioned in the preceding report; except that the first report filed pursuant to this title shall contain the name and address of each person who has made any contribution of $500 or more to such person since the effective date of this title;
“(2) the total sum of the contributions made to or for such person during the calendar year and not stated under paragraph (1) ;
“ (3) the total sum of all contributions made to or for such person during the calendar year;
“ (4) the name and address of each person to whom an expenditure in one or more items of the aggregate amount or value, within the calendar year, of $10 or more has been made by or on behalf of such person, and the amount, date, and purpose of such expenditure;
“(5) the total sum of all expenditures made by or on behalf of such person during the calendar year and not stated under paragraph (4);
“(6) the total sum of expenditures made by or on behalf of such person during the calendar year.
“(b) The statements required to be filed by subsection (a) shall be cumulative during the calendar year to which they relate, but where *615there has been no change in an item reported in a previous statement only the amount need be carried forward.”
The following are “the purposes designated in subparagraph (a) or (b) of section 307”:
“(a) The passage or defeat of any legislation by the Congress of the United States.
“(b) To influence, directly or indirectly, the passage or defeat of any legislation by the Congress of the United States.”
Section 308 provides:
“(a) Any person who shall engage himself for pay or for any consideration for the purpose of attempting to influence the passage or defeat of any legislation by the Congress of the United States shall, before doing anything in furtherance of such object, register with the Clerk of the House of Representatives and the Secretary of the Senate and shall give to those officers in writing and under *616oath, his name and. business address, the name and address of the person by whom he is employed, and in whose interest he appears or works, the duration of such employment, how much he is paid and is to receive, by whom he is paid or is to be paid, how much he is to be paid for expenses, and what expenses are to be included. Each such person so registering shall, between the first and tenth day of each calendar quarter, so long as his activity continues, file with the Clerk and Secretary a detailed report under oath of all money received and expended by him during the preceding calendar quarter in carrying on his work; to whom paid; for what purposes; and the names of any papers, periodicals, magazines, or other publications in which he has caused to be published any articles or editorials; and the proposed legislation he is employed to support or oppose. The provisions of this section shall not apply to any person who merely appears before a committee of the Congress of the United States in support of or opposition to legislation; nor to any public official acting in his official capacity; nor in the case of any newspaper or other regularly published periodical (including any individual who owns, publishes, or is employed by any such newspaper or periodical) which in the ordinary course of business publishes news items, editorials, or other comments, or paid advertisements, which directly or indirectly urge the passage or defeat of legislation, if such newspaper, periodical, or individual, engages in no further or other activities in connection with the passage or defeat of such legislation, other than to appear before a committee of the Congress of the United States in support of or in opposition to such legislation.
“(b) All information required to be filed under the provisions of this section with the Clerk of the House of Representatives and the Secretary of the Senate shall be compiled by said Clerk and Secretary, acting jointly, as soon as practicable after the close of the calendar quarter with respect to which such information is filed and shall be printed in the Congressional Record.”
A third count under § 308 was abated on the death of the defendant against whom the charge was made.
18 U. S. C. § 3731. See United States v. Petrillo, 332 U. S. 1, 5. For “The Government’s appeal does not open the whole case.” United States v. Borden Co., 308 U. S. 188, 193.
See Jordan v. De George, 341 U. S. 223, 230-232; Quarles, Some Statutory Construction Problems and Approaches in Criminal Law, 3 Vand. L. Rev. 531, 539-543; Note, 62 Harv. L. Rev. 77.
Cf. Fox v. Washington, 236 U. S. 273; Musser v. Utah, 333 U. S. 95; Winters v. New York, 333 U. S. 507, 510.
This rule as to statutes charged with vagueness is but one aspect of the broader principle that this Court, if fairly possible, must construe congressional enactments so as to avoid a danger of unconstitutionality. United States v. Delaware & Hudson Co., 213 U. S. 366, 407-408; United States v. Congress of Industrial Organizations, 335 U. S. 106, 120-121; United States v. Rumely, 345 U. S. 41, 47. Thus, in the C. I. O. case, supra, this Court held that expenditures by a labor organization for the publication of a weekly periodical urging support for a certain candidate in a forthcoming congressional election were not forbidden by the Federal Corrupt Practices Act, which makes it unlawful for “. . . any labor organization to make a contribution or expenditure in connection with any [congressional] election . . . .” Similarly, in the Rumely case, supra, this Court construed a House Resolution authorizing investigation of “all lobbying activities intended to influence, encourage, promote, or retard legislation” to cover only “ ‘lobbying in its commonly accepted sense,’ that is, ‘representations made directly to the Congress, its members, or its committees.’ ”
Section 302 (c) defines the term “person” as including “an individual, partnership, committee, association, corporation, and any other organization or group of persons.”
The Government’s view is based on a variance between the language of § 307 and the language of § 305. Section 307 refers to any person who “solicits, collects, or receives” contributions; §305, however, refers not only to “receiving any contributions” but also to “expending any money.” It is apparently the Government’s contention that § 307 — since it makes no reference to expenditures — is inapplicable to the expenditure provisions of § 305. Section 307, however, limits the application of § 305 as a whole, not merely a part of it.
Both the Senate and House reports on the bill state that “This section [§ 307] defines the application of the title S. Rep. No. 1400, 79th Cong., 2d Sess., p. 28; Committee Print, July 22, 1946, statement by Representative Monroney on Legislative Reorganization Act of 1946, 79th Cong., 2d Sess., p. 34. See also the remarks of Representative Dirksen in presenting the bill to the House: “The gist of the antilobbying provision is contained in section 307.” 92 Cong. Rec. 10088.
The Lobbying Act was enacted as Title III of the Legislative Reorganization Act of 1946, which was reported to Congress by the Joint Committee on the Organization of Congress. The Senate and House reports accompanying the bill were identical with respect to *621Title III. Both declared that the Lobbying Act applies “chiefly to three distinct classes of so-called lobbyists:
“First. Those who do not visit the Capitol but initiate propaganda from all over the country in the form of letters and telegrams, many of which have been based entirely upon misinformation as to facts. This class of persons and organizations will be required under the title, not to cease or curtail their activities in any respect, but merely to disclose the sources of their collections and the methods in which they are disbursed.
“Second. The second class of lobbyists are those who are employed to come to the Capitol under the false impression that they exert some powerful influence over Members of Congress. These individuals spend their time in Washington presumably exerting some mysterious influence with respect to the legislation in which their employers are interested, but carefully conceal from Members of Congress whom they happen to contact the purpose of their presence. The title in no wise prohibits or curtails their activities. It merely requires that they shall register and disclose the sources and purposes of their employment and the amount of their compensation.
“Third. There is a third class of entirely honest and respectable representatives of business, professional, and philanthropic organizations who come to Washington openly and frankly to express their views for or against legislation, many of whom serve a useful and perfectly legitimate purpose in expressing the views and interpretations of their employers with respect to legislation which concerns them. They will likewise be required to register and state their compensation and the sources of their employment.”
S. Rep. No. 1400, 79th Cong., 2d Sess., p. 27; Committee Print, July 22, 1946, statement by Representative Monroney on Legislative Reorganization Act of 1946, 79th Cong., 2d Sess., pp. 32-33. See also the statement in the Senate by Senator La Follette, who was Chairman of the Joint Committee, at 92 Cong. Rec. 6367-6368.
See the Act’s separability clause, note 18, infra, providing that the invalidity of any application of the Act should not affect the validity of its application “to other persons and circumstances.”
Both the Senate and House reports accompanying the bill state that the Act "... does not apply to organizations formed for other purposes whose efforts to influence legislation are merely incidental to the purposes for which formed.” S. Hep. No. 1400, 79th Cong., 2d Sess., p. 27; Committee Print, July 22, 1946, statement by Representative Monroney on Legislative Reorganization Act of 1946, 79th Cong., 2d Sess., p. 32. In the Senate discussion preceding enactment, Senator Hawkes asked Senator La Follette, Chairman of the Joint Committee in charge of the bill, for an explanation of the “principal purpose” requirement. In particular, Senator Hawkes sought assurance that multi-purposed organizations like the United States Chamber of Commerce wopld not be subject to the Act. Senator La Follette refused to give such assurance, stating: “So far as any organizations or individuals are concerned, I will say to the Senator from New Jersey, it will depend on the type and character of activity which they undertake. ... I cannot tell the Senator whether they will come under the act. It will depend on the type of activity in which they engage, so far as legislation is concerned. ... It [the Act] affects all individuals and organizations alike if they engage in a covered activity.” (Italics added.) 92 Cong. Rec. 10151-10152. See also Representative Dirksen’s remarks in the House, 92 Cong. Rec. 10088.
Such a criterion is not novel in federal law. See Int. Rev. Code, § 23 (o) (2) (income tax), § 812 (d) (estate tax), and § 1004 (a) (2) (B) (gift tax), providing tax exemption for contributions to charitable and educational organizations “no substantial part of the activities of which is carrying on propaganda, or otherwise attempting, to influence legislation.” For illustrative cases applying this criterion, see *623Sharpe’s Estate v. Commissioner, 148 F. 2d 179 (C. A. 3d Cir.); Marshall v. Commissioner, 147 F. 2d 75 (C. A. 2d Cir.); Faulkner v. Commissioner, 112 F. 2d 987 (C. A. 1st Cir.); Huntington National Bank v. Commissioner, 13 T. C. 760, 769. Cf. Girard Trust Co. v. Commissioner, 122 F. 2d 108 (C. A. 3d Cir.); Leuhuscher v. Commissioner, 54 F. 2d 998 (C. A. 2d Cir.); Weyl v. Commissioner, 48 F. 2d 811 (C. A. 2d Cir.); Slee v. Commissioner, 42 F. 2d 184 (C. A. 2d Cir.). See also Annotation, 138 A. L. R. 456.
For the three exceptions, see note 2, supra.
Under this construction, the Act is at least as definite as many other criminal statutes which this Court has upheld against a charge of vagueness. E. g., Boyce Motor Lines v. United States, 342 U. S. 337 (regulation providing that drivers of motor vehicles carrying explosives “shall avoid, so far as practicable, and, where feasible, by prearrangement of routes, driving into or through congested thoroughfares, places where crowds are assembled, street car tracks, tunnels, viaducts, and dangerous crossings”); Dennis v. United States, 341 U. S. 494 (Smith Act making it unlawful for any person to conspire “to knowingly or willfully advocate, abet, advise, or teach the duty, necessity, desirability, or propriety of overthrowing or destroying any government in the United States by force or violence . . . ."); United States v. Petrillo, 332 U. S. 1 (statute forbidding coercion of radio stations to employ persons “in excess of the number of employees needed ... to perform actual services”); Screws v. United States, 325 U. S. 91, and Williams v. United States, 341 U. S. 97 (statute forbidding acts which would deprive a person of “any rights, privileges, or immunities secured or protected by the Constitution and laws of the United States”); United States v. Wurzbach, 280 U. S. 396 (statute forbidding any candidate for Congress or any officer or employee of the United States to solicit or receive a “contribution for any political purpose whatever” from any other such officer or employee); Omaechevarria v. Idaho, 246 U. S. 343 (statute forbidding pasturing of sheep “on any cattle range previously occupied by cattle, or upon any range usually occupied by any cattle grower”); Fox v. Washington, 236 U. S. 273 (state statute imposing criminal sanctions on “Every person who shall wilfully print, publish, edit, issue, or knowingly circulate, sell, distribute or display any book, paper, document, or written or printed matter, in any form, advocating, encouraging or inciting, or having a tendency to encourage or incite the commission of any crime, breach of the peace or act of violence, or which shall tend to encourage or advocate disrespect for law or for any court or courts of justice . . . .”); Nash v. United States, 229 U. S. 373 (Sherman Act forbidding “Every contract, combination in the form of trust or otherwise, or conspiracy, in restraint *625of trade or commerce among the several States, or with foreign nations”). Cf. Jordan v. De George, 341 U. S. 223 (statute providing for deportation of persons who have committed crimes involving “moral turpitude”).
Similar legislation has been enacted in over twenty states. See Notes, 56 Yale L. J. 304, 313-316, and 47 Col. L. Rev. 98, 99-103.
Similarly, the Hatch Act probably deters some federal employees from political activity permitted by that statute, but yet was sustained because of the national interest in a nonpolitical civil service. United Public Workers v. Mitchell, 330 U. S. 75.
60 Stat. 812, 814:
“If any provision of this Act or the application thereof to any person or circumstances is held invalid, the validity of the remainder of the Act and of the application of such provision to other persons and circumstances shall not be affected thereby.”