United States v. Reilly was a United States Supreme Court case that dealt with the issue of whether a federal court had the authority to issue a writ of habeas corpus to a state prisoner. The case involved a man named John Reilly, who had been convicted of murder in the state of New York and sentenced to life in prison. The Supreme Court held that the federal court did not have the authority to issue a writ of habeas corpus to a state prisoner. The Court reasoned that the writ of habeas corpus was a remedy that was available only to federal prisoners, and that the federal court did not have the power to interfere with the state's criminal justice system. The Court also noted that the writ of habeas corpus was a remedy that was available only in cases where the prisoner had been denied due process of law. The Court's decision in United States v. Reilly was significant because it established that the federal court did not have the authority to interfere with the state's criminal justice system. This decision has been cited in numerous cases since then, and it has been used to support the idea that the federal court should not interfere with the state's criminal justice system.

In United States v. Reilly, the Supreme Court was tasked with determining whether a federal statute that imposed an additional tax on certain corporations applied to a corporation in which one of its shareholders had died and his estate owned shares. The majority opinion held that the statute did apply to such cases, but Justice Field dissented from this decision. He argued that when Congress passed the law it intended for it to only be applicable when all of the shareholders were living persons; thus, he concluded that applying it in this case would be contrary to Congressional intent and therefore unconstitutional. Furthermore, he noted that if Congress wanted estates or other entities like them included within its scope they could have easily done so by using language more appropriate for such situations than what was used in their original legislation. In conclusion, Justice Field believed there should have been no additional taxes imposed on Reilly's corporation due to his shareholder's death as doing so would violate both congressional intent and constitutional principles