In the United States v. Pena case of 1899, the U.S. Supreme Court ruled on a matter concerning customs duties and importation laws. The defendant, Mr. Pena, was charged with smuggling goods into the country without paying required customs duties and for making false statements about said goods to avoid these payments. He argued that he had not violated any law because at the time of his actions there were no existing statutes imposing penalties for such conduct in Puerto Rico where he resided - this being after Spain ceded control over Puerto Rico to America but before Congress enacted specific legislation governing it. The court disagreed with Pena's argument stating that upon acquisition by treaty or conquest, territories automatically fall under jurisdiction of American revenue laws unless explicitly exempted by Congress; hence even though no new rules were made specifically for Puerto Rico immediately after its annexation, existing federal laws still applied there including those related to customs duty evasion which Mr.Pena was accused of violating. Thus upholding lower courts' decisions convicting him on all counts,the Supreme Court affirmed that territorial acquisitions are subject to U.S federal law from moment they become part of national domain unless otherwise specified by legislative action.

The dissenting opinion in the United States v. Pena case argued that the majority's decision was a misinterpretation of the law and an overreach of federal power. The dissenting justices believed that Congress did not have authority to regulate local trade within territories, as it does with states, under its constitutional powers. They contended that this interpretation expanded federal jurisdiction beyond what was intended by the Constitution's framers and could lead to potential abuses of power. Furthermore, they disagreed with applying laws retroactively; in this case, making Pena liable for actions committed before legislation passed criminalizing them. This view held such retrospective application violated principles of fairness and due process rights protected by Fifth Amendment guarantees against ex post facto laws or punishments after-the-fact for acts previously legal when committed.