The Eliza Hancox case 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 federal custody. The case arose when Eliza Hancox, a prisoner in the custody of the United States Marshal, sought a writ of habeas corpus from the state court of Alabama. The United States Marshal argued that the state court did not have the authority to issue the writ, as the prisoner was in federal custody. The Supreme Court ultimately held that the state court did not have the authority to issue the writ, as the power to issue writs of habeas corpus was exclusively vested in the federal courts. The Court reasoned that the power to issue writs of habeas corpus was a part of the federal judicial power, and that the state courts did not have the authority to exercise such power. The Court further held that the state court's attempt to issue the writ was an unconstitutional interference with the federal judicial power.

In the case of The Eliza Hancox, Justice Field delivered a dissenting opinion. He argued that the majority's decision was contrary to both common sense and established legal precedent. According to him, it was clear from the facts of this case that there had been an implied contract between Eliza Hancox and her employer for her services as a nursemaid. Furthermore, he noted that under existing law such contracts were enforceable even if they lacked consideration or formalities like writing or sealing. As such, he concluded that Eliza should have been allowed to recover damages for breach of contract in this instance since she had performed all her duties faithfully but still not received payment for them.