The case involved a criminal prosecution under the 1934 National Firearms Act (NFA). Passed in response to public outcry over the St. Valentine's Day Massacre, the NFA requires certain types of firearms, such as fully automatic firearms and short-barrelled rifles and shotguns, to be registered with the Miscellaneous Tax Unit, which was later folded into what eventually became the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), then part of the Bureau of Internal Revenue, the ancestor of today's Internal Revenue Service. The $200 tax was to be paid at the time of registration and again if the firearm was ever sold.