2 U.S.C. § 441c : US Code - Section 441C: Contributions by government contractors

    (a) Prohibition
      It shall be unlawful for any person - 
        (1) who enters into any contract with the United States or any
      department or agency thereof either for the rendition of personal
      services or furnishing any material, supplies, or equipment to
      the United States or any department or agency thereof or for
      selling any land or building to the United States or any
      department or agency thereof, if payment for the performance of
      such contract or payment for such material, supplies, equipment,
      land, or building is to be made in whole or in part from funds
      appropriated by the Congress, at any time between the
      commencement of negotiations for and the later of (A) the
      completion of performance under; or (B) the termination of
      negotiations for, such contract or furnishing of material,
      supplies, equipment, land, or buildings, directly or indirectly
      to make any contribution of money or other things of value, or to
      promise expressly or impliedly to make any such contribution to
      any political party, committee, or candidate for public office or
      to any person for any political purpose or use; or
        (2) knowingly to solicit any such contribution from any such
      person for any such purpose during any such period.
    (b) Separate segregated funds
      This section does not prohibit or make unlawful the establishment
    or administration of, or the solicitation of contributions to, any
    separate segregated fund by any corporation, labor organization,
    membership organization, cooperative, or corporation without
    capital stock for the purpose of influencing the nomination for
    election, or election, of any person to Federal office, unless the
    provisions of section 441b of this title prohibit or make unlawful
    the establishment or administration of, or the solicitation of
    contributions to, such fund. Each specific prohibition, allowance,
    and duty applicable to a corporation, labor organization, or
    separate segregated fund under section 441b of this title applies
    to a corporation, labor organization, or separate segregated fund
    to which this subsection applies.
    (c) "Labor organization" defined
      For purposes of this section, the term "labor organization" has
    the meaning given it by section 441b(b)(1) of this title.