Whether the National Firearms Act was an unconstitutional exercise of a general police power reserved to the States rather than a valid federal revenue measure.
Holding
No. The Act was a valid exercise of Congress's taxing power.
Reasoning
The Court treated the objection as foreclosed by its prior decisions upholding federal tax statutes that regulate conduct while raising revenue. In particular, Sonzinsky v. United States had sustained the National Firearms Act's taxing structure, and the Court's decisions under the Harrison Narcotic Act likewise recognized that a revenue measure does not become invalid merely because it has regulatory effects.
Because the Act imposed taxes and used registration, documentation, and interstate-transport restrictions to enforce that tax scheme, Congress had not impermissibly assumed the States' general police power. The Court therefore described the federalism objection as plainly untenable.