The Neptune, Harrod et al. Claimants was a case heard before the United States Supreme Court in 1818. The claimants were merchants who had purchased goods from France during the Napoleonic Wars and sought to be compensated for their losses when they could not receive payment due to an embargo imposed by President Thomas Jefferson on all vessels coming from or going to French ports. The court held that while Congress has authority over foreign commerce, it cannot interfere with private contracts between individuals and foreign nations unless there is a clear violation of public policy or law. Furthermore, the court found that since no such violation existed here, any interference with these contracts would constitute an unconstitutional taking of property without just compensation in contravention of Article III Section 8 Clause 9 of the Constitution which states “No Preference shall be given by any Regulation of Commerce or Revenue to the Ports of one State over those another; nor shall Vessels bound to, or from one State be obliged enter into another” Thus, because there was no legal basis for interfering with these contracts between individuals and foreign nations as well as violating constitutional provisions protecting interstate commerce rights ,the court ruled in favor of allowing compensation for damages incurred due to Jefferson's embargo order .

In The Neptune, Harrod et al. Claimants case, the Supreme Court was tasked with determining whether a ship and its cargo were rightfully seized by the United States Navy during wartime. The majority opinion held that since the vessel had been captured in an area of hostilities between France and England, it could be considered enemy property subject to seizure under international law. However, Justice Johnson dissented from this ruling on two grounds: firstly, he argued that there was no evidence presented at trial to prove that any hostile acts had actually taken place in the region; secondly, even if such acts did occur they would not have justified seizing a neutral vessel like The Neptune as it posed no threat or danger to either belligerent nation. He concluded his dissent by stating that while war may give rise to certain rights of capture over enemy vessels which are actively engaged in hostility against one's own countrymen or allies - these rights do not extend so far as to include innocent neutrals who pose no threat whatsoever.