Mace v. Merrill 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 mandamus to a federal court. The case arose when the plaintiff, Mace, sought to compel the defendant, Merrill, to issue a writ of mandamus to the federal court. The plaintiff argued that the state court had the authority to issue the writ of mandamus because the federal court had failed to act on a case that had been pending before it for several years. The Supreme Court held that the state court did not have the authority to issue the writ of mandamus because the federal court had exclusive jurisdiction over the case. The Court reasoned that the state court lacked the power to interfere with the federal court's jurisdiction and that the writ of mandamus was an inappropriate remedy for the plaintiff's complaint. The Court also noted that the plaintiff had other remedies available to him, such as filing a petition for a writ of mandamus in the federal court. As a result, the Supreme Court affirmed the decision of the lower court and held that the state court did not have the authority to issue the writ of mandamus.

Justice Field wrote the dissenting opinion in Mace v. Merrill, arguing that the majority's decision was not supported by precedent or logic. He argued that a contract between two parties should be enforced according to its terms and conditions, regardless of whether it is beneficial for one party over another. In this case, he believed that the contract between Mace and Merrill should have been upheld as written because it had already been accepted by both parties when they entered into it. Furthermore, Justice Field noted that if contracts could be voided simply because one party found them unfavorable after entering into them then no contracts would ever be enforceable since all parties are likely to find some parts of any agreement disadvantageous at some point in time. Therefore, he concluded that the court should have respected their original agreement and enforced its terms accordingly rather than allowing either side to unilaterally void it due to later dissatisfaction with certain aspects of their bargain.