§ 1653
Aliens as pirates
Official text prohibited actmental stateif conditionpenaltylegal term
Whoever, being a citizen or subject of any foreign state, is found and taken on the sea making war upon the United States, or cruising against the vessels and property thereof, or of the citizens of the same, contrary to the provisions of any treaty existing between the United States and the state of which the offender is a citizen or subject, when by such treaty such acts are declared to be piracy, is a pirate, and shall be imprisoned for life.
History: (June 25, 1948, ch. 645, 62 Stat. 774 (PDF, 39 MB).)
Simplified explanation
It is a federal crime for a citizen of a foreign country to make war on the United States, or attack U.S. or U.S. citizens' ships and property at sea, when a treaty with that country calls such acts piracy.