In Nigro v. United States, the Supreme Court upheld a conviction under the Harrison Narcotics Tax Act of 1914. The defendant, Frank Nigro, was convicted for selling derivatives of opium and coca leaves without having paid the special tax imposed by this act. He argued that Congress had exceeded its constitutional power to regulate interstate commerce and levy taxes with this legislation because it effectively prohibited trade in narcotics rather than merely regulating or taxing it. However, Justice McReynolds delivered an opinion on behalf of a unanimous court rejecting these arguments. The court held that even if Congress' primary aim was to prohibit such trade altogether, it could do so as long as there were some legitimate regulatory or revenue-raising purpose behind its actions - which there clearly was in this case given the serious public health issues associated with drug abuse.

In the dissenting opinion for Nigro v. United States, Justice McReynolds disagreed with the majority's interpretation of Congress' power under the Commerce Clause. He argued that while Congress has broad authority to regulate interstate commerce, it does not have unlimited power to prohibit or criminalize activities merely because they may indirectly affect commerce between states. In this case, he believed that Congress had overstepped its bounds by making all dealings in narcotics a federal crime regardless of whether they involved interstate trade or not. According to Justice McReynolds, such an expansive reading of the Commerce Clause would essentially give Congress police powers reserved for individual states under Tenth Amendment and undermine principles of federalism embedded in Constitution.