26 U.S.C. § 5861: Prohibited acts

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 to receive or possess a firearm transferred to him in violation of the provisions of this chapter; or to receive or possess a firearm made in violation of the provisions of this chapter; or to receive or possess a firearm which is not registered to him in the National Firearms Registration and Transfer Record; or to transfer a firearm in violation of the provisions of this chapter; or to make a firearm in violation of the provisions of this chapter; or to obliterate, remove, change, or alter the serial number or other identification of a firearm required by this chapter; or to receive or possess a firearm having the serial number or other identification required by this chapter obliterated, removed, changed, or altered; or to receive or possess a firearm which is not identified by a serial number as required by this chapter; or to transport, deliver, or receive any firearm in interstate commerce which has not been registered as required by this chapter; or to receive or possess a firearm which has been imported or brought into the United States in violation of section 5844; or 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.