The United States v. The Brigantine Mars was a Supreme Court case that considered the legality of an act of Congress passed in 1812, which authorized the President to seize and confiscate any vessel owned by citizens of France or its allies if they were found within U.S. waters during wartime with France. In this particular case, a French-owned brigantine called "Mars" had been seized by American authorities while it was anchored off the coast of New Jersey during war time with France. The court held that Congress had acted constitutionally when passing this law and thus affirmed the seizure as valid under international law principles at that time; however, it also noted that such seizures could only be made for legitimate purposes related to national security and not simply out of spite or malice towards foreign nations or their citizens.

In United States v. The Brigantine Mars, the Supreme Court was tasked with determining whether a vessel that had been captured by an American privateer during the War of 1812 could be condemned as a prize of war. In its decision, Justice Story delivered a dissenting opinion in which he argued that Congress had not authorized such captures and thus they were illegal under international law. He further noted that even if Congress did authorize such captures, it would still be necessary to prove beyond reasonable doubt that the vessel was actually engaged in hostile operations against America before it could be legally seized and condemned as a prize of war. As no evidence existed to support this claim, Justice Story concluded that condemnation should not have been granted for this particular case.