The United States v. Smith was a case heard by the Supreme Court in 1820. The defendant, William Smith, had been convicted of violating the Non-Intercourse Act which prohibited trade with certain foreign nations and imposed penalties for violations of its provisions. The issue before the court was whether or not Congress had authority to pass such an act under their power to regulate commerce among foreign nations and between states. In a unanimous decision, Chief Justice John Marshall held that Congress did indeed have this power as it is granted by Article I Section 8 Clause 3 of the Constitution known as "the Commerce Clause." He further stated that while some aspects of international relations may be beyond Congressional control, regulating commercial intercourse between different countries falls within their purview and thus they are able to pass laws like those found in the Non-Intercourse Act without infringing on any other branch's powers or rights. This ruling established an important precedent regarding congressional authority over interstate commerce which has since been cited numerous times throughout American legal history.

In The United States v. Smith, the Supreme Court was tasked with determining whether a defendant could be convicted of an offense that had been committed before Congress passed a law criminalizing it. Chief Justice John Marshall wrote the dissenting opinion, arguing that retroactive application of laws is unconstitutional and violates due process rights. He argued that if Congress can pass laws making something illegal after it has already occurred, then individuals have no way to know what conduct will be considered criminal in advance and cannot plan their lives accordingly. Furthermore, he argued that such retroactivity would lead to arbitrary punishments since those who committed similar offenses at different times may face vastly different consequences for their actions depending on when they were charged or tried. Ultimately, Marshall concluded by asserting his belief that “no legislative act contrary to the Constitution can be valid” and thus any attempt by Congress to make an action illegal after it has already taken place should not stand as constitutional law.