Smith v. Mors was a United States Supreme Court case that dealt with the issue of whether a state court had the authority to issue a writ of habeas corpus to a prisoner held in a federal prison. The case arose when a prisoner, Smith, was held in a federal prison in New York and sought a writ of habeas corpus from the state court. The state court granted the writ, and the federal government appealed the decision to the Supreme Court. The Supreme Court held that the state court did not have the authority to issue the writ of habeas corpus. The Court reasoned that the writ of habeas corpus was a federal power, and that the state court did not have the authority to interfere with the federal government's power to imprison individuals. The Court also noted that the writ of habeas corpus was a fundamental right, and that the state court should not be allowed to interfere with the federal government's power to imprison individuals. The Court's decision in Smith v. Mors established that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in a federal prison. This decision has been cited in numerous cases since then, and has been used to support the idea that the federal government has the power to imprison individuals without interference from the state court.

In Smith v. Mors, the Supreme Court was asked to decide whether a federal court had jurisdiction over a case involving an alleged violation of the Fugitive Slave Act of 1850. The majority opinion held that it did not have such jurisdiction because Congress had not given any authority for such cases to be heard in federal courts. Justice Field dissented from this decision, arguing that Congress had indeed granted federal courts with power to hear these types of cases and thus they should have been allowed to do so in this instance as well. He argued that if state laws were found unconstitutional or violated national law then it was within the purview of the federal government and its judiciary branch to adjudicate them accordingly. Furthermore, he noted that since slavery was abolished by constitutional amendment there could be no doubt about its illegality under both state and national law; therefore, any violations thereof should fall under the jurisdiction of a higher court than those at the state level alone.