In La Roque v. United States (1915), the U.S. Supreme Court ruled on a case involving the application of federal law in Puerto Rico, an unincorporated territory of the United States. The plaintiff, Mr. La Roque, argued that certain provisions of the Foraker Act - which established a civilian government in Puerto Rico after its acquisition from Spain - were unconstitutional because they imposed duties and tariffs on goods transported between Puerto Rico and mainland U.S., contrary to Article I Section 8 Clause 1 of the Constitution which prohibits Congress from imposing taxes or duties on articles exported from any state. The court disagreed with Mr. La Roque's argument stating that while it was true that Congress could not impose such restrictions among states, this did not apply to territories like Puerto Rico as they are not considered part of "the Union" under constitutional terms but belong to it by virtue of territorial possession. Therefore, according to this ruling, Congress had broad discretion over how it governed these territories including imposing tariffs or other economic regulations without violating constitutional principles applicable within states.

In the dissenting opinion for La Roque v. United States, Justice Holmes disagreed with the majority's ruling that a federal law prohibiting lotteries applied to Puerto Rico. He argued that Congress did not intend for this law to apply to territories like Puerto Rico when it was passed in 1895, as these areas were not yet part of the U.S. Furthermore, he contended that even if Congress had intended for such laws to extend automatically to new territories, they should have made this clear in their legislation instead of leaving it up to judicial interpretation. Holmes also pointed out inconsistencies in how similar cases involving other territories had been handled by the court and suggested that these discrepancies undermined its decision in this case.