26 U.S.C. § 5861 : US Code - Section 5861: Prohibited acts

      It shall be unlawful for any person - 
        (a) to engage in business as a manufacturer or importer of, or
      dealer in, firearms without having paid the special
      (occupational) tax required by section 5801 for his business or
      having registered as required by section 5802; or
        (b) to receive or possess a firearm transferred to him in
      violation of the provisions of this chapter; or
        (c) to receive or possess a firearm made in violation of the
      provisions of this chapter; or
        (d) to receive or possess a firearm which is not registered to
      him in the National Firearms Registration and Transfer Record; or
        (e) to transfer a firearm in violation of the provisions of
      this chapter; or
        (f) to make a firearm in violation of the provisions of this
      chapter; or
        (g) to obliterate, remove, change, or alter the serial number
      or other identification of a firearm required by this chapter; or
        (h) to receive or possess a firearm having the serial number or
      other identification required by this chapter obliterated,
      removed, changed, or altered; or
        (i) to receive or possess a firearm which is not identified by
      a serial number as required by this chapter; or
        (j) to transport, deliver, or receive any firearm in interstate
      commerce which has not been registered as required by this
      chapter; or
        (k) to receive or possess a firearm which has been imported or
      brought into the United States in violation of section 5844; or
        (l) to make, or cause the making of, a false entry on any
      application, return, or record required by this chapter, knowing
      such entry to be false.