The Gray Jacket was a Supreme Court case in which the court held that Congress had no power to pass laws regulating slavery within states. The case arose from an act of Congress passed during the Civil War, which prohibited any person from wearing or carrying arms while engaged in insurrection against the United States government. The plaintiff argued that this law violated his rights under the Fifth Amendment by depriving him of property without due process of law and interfering with state sovereignty over its own internal affairs. In a 5-4 decision, Chief Justice Salmon P. Chase wrote for the majority opinion that Congress did not have authority to regulate slavery within states because it was beyond their enumerated powers granted by Article I, Section 8 of the Constitution. He further stated that such regulation would be unconstitutional as it would interfere with state sovereignty and violate principles established in prior cases like Prigg v Pennsylvania (1842). Ultimately, this ruling affirmed limits on congressional power when dealing with matters related to domestic policy and individual liberties protected by constitutional amendments like due process protections found in the Fifth Amendment.

In The Gray Jacket, the Supreme Court was tasked with deciding whether a slave who had been taken to Illinois and held there for two years could be considered free under the state's laws. The majority opinion found that since slavery was prohibited in Illinois, the man should be declared free. However, Justice Swayne dissented from this ruling on several grounds. He argued that Congress had exclusive power over interstate commerce and thus any decision regarding freedom of slaves must come from them rather than individual states. Furthermore, he noted that while slavery may have been illegal in Illinois at the time of his arrival there, it did not necessarily mean he would remain free if returned to another state where it was still legal. Finally, Swayne contended that even if Congress were to pass legislation allowing slaves brought into non-slaveholding states to become emancipated after a certain period of time spent there - as some proposed bills sought to do - such an act would violate both natural law and constitutional principles by depriving owners of their property without due process or compensation.