In the case of United States v. Heinszen & Company, 1906, the U.S. Supreme Court ruled on a dispute involving customs duties imposed by American military authorities in the Philippines during wartime conditions prior to civil government establishment. The defendant, Heinszen & Co., was an import-export business that refused to pay these duties arguing they were unconstitutional as Congress had not authorized them and violated international law because they were excessive for military contributions in occupied territory. However, the court upheld their legality under war powers granted by Article I Section 8 Clause 11 of the Constitution (the Declare War Clause), which allowed such impositions until peace treaties are ratified or civil governments established. Furthermore, it found no violation of international law since there is no fixed limit on what constitutes reasonable levies in occupied territories; this depends upon circumstances and good faith judgment from occupying forces' commanders.

In the dissenting opinion for United States v. Heinszen & Company, Justice Harlan argued that the majority's decision was inconsistent with both international law and U.S. constitutional principles. He contended that it was improper to apply a war revenue statute retroactively to transactions completed before its enactment, as this violated basic notions of fairness and due process rights protected by the Constitution. Furthermore, he disagreed with the majority's interpretation of "enemy" in wartime legislation, asserting that such laws should not be applied against neutral parties who were merely conducting business in enemy territory without any intent or action supporting enemy forces. In his view, applying these laws so broadly would discourage trade and harm American interests abroad while also violating international norms respecting neutrality during armed conflicts.