National Firearms Act is an American law passed in 1934 that mandates the registration of all Act Two weapons - that is, all sound suppressors or 'silencers', all fully-automatic and burst-fire firearms, all rifles and shotguns with a barrel length of less than 18 inches, or overall length of less than 26 inches. For weapons with folding, collapsing or telescoping stocks, the overall length with the stock collapsed/fully retracted must be at least 26 inches.

All such items must be registered with the BATF, and initial registration required the payment of $200 for a special BATF tax stamp. Additionally, each time an Act Two weapon is transfered to another person, an additional $200 tax must be paid by the reciever, for each item.

The law was found to be unconstitutional in State vs. Miller, though the ruling was overturned on appeal to the Supreme Court as the defendant failed to appear, and no brief was filled on Miller's behalf.