In Sonzinsky v. United States, the Supreme Court upheld a federal tax on firearms dealers as constitutional. The petitioner, Joseph Sonzinsky, was indicted for not paying this tax and argued that it was an unconstitutional attempt by Congress to regulate activities reserved to the states under the Tenth Amendment. However, the court ruled unanimously against him stating that there is no provision in the Constitution which could be interpreted as prohibiting Congress from levying such a tax or requiring them to show any specific purpose behind it other than revenue generation. They further stated that if every federal law affecting commerce had to be justified by some direct effect on interstate trade then almost all of its powers would become invalid because they indirectly affect commerce too.

In the dissenting opinion for Sonzinsky v. United States, Justice McReynolds argued that the tax in question was not a true revenue-raising measure but rather an attempt to regulate and suppress firearm traffic under the guise of taxation. He contended that this violated the Tenth Amendment by infringing on states' rights to control their own internal affairs, including regulation of firearms. Furthermore, he believed it also overstepped Congress's constitutional authority as defined by Article I Section 8 which grants Congress power "to lay and collect Taxes" but does not allow them to use this power as a means of controlling activities reserved for state governments or individuals. Thus, according to Justice McReynolds’ interpretation, using taxation powers in such a way would be unconstitutional.