Seymour v. Freer 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 the state of New York issued a writ of habeas corpus to a prisoner held in a federal prison in New York. The prisoner, Seymour, argued that the state court did not have the authority to issue the writ because the federal government had exclusive jurisdiction over the prison. The Supreme Court agreed with Seymour, ruling that the state court did not have the authority to issue the writ. The Court held that the federal government had exclusive jurisdiction over federal prisons and that the state court could not interfere with the federal government's authority. The Court also held that the writ of habeas corpus was a federal remedy and that the state court could not issue it. This decision established the principle that the federal government has exclusive jurisdiction over federal prisons and that state courts cannot interfere with the federal government's authority.

In Seymour v. Freer, the Supreme Court was tasked with determining whether a contract between two parties could be enforced when it had been made in violation of an existing state law. The majority opinion held that the contract should not be enforced because it violated public policy and would encourage further violations of the law. Justice Field dissented from this decision, arguing that contracts are generally enforceable unless they violate some fundamental principle of justice or morality or involve matters which have been placed under governmental control by statute or otherwise. He argued that since there were no such principles at play in this case, enforcing the contract would not lead to any negative consequences and thus should be allowed to stand as valid despite its violation of state law.