Mower v. Fletcher was a United States Supreme Court case that addressed the issue of whether a state court had the authority to grant a new trial in a case that had already been decided by a federal court. The case arose when the plaintiff, Mower, sued the defendant, Fletcher, in a state court for breach of contract. The state court found in favor of Mower and awarded him damages. Fletcher then appealed the decision to a federal court, which affirmed the state court's decision. Fletcher then sought a new trial in the state court, arguing that the federal court had erred in its decision. The Supreme Court held that the state court did not have the authority to grant a new trial in a case that had already been decided by a federal court. The Court reasoned that the state court was bound by the decision of the federal court and could not grant a new trial. The Court further held that the state court was not authorized to review the decision of the federal court and could not grant a new trial on the basis of any alleged errors in the federal court's decision. The Court concluded that the state court lacked the authority to grant a new trial in the case.

Justice Field delivered the dissenting opinion in Mower v. Fletcher, arguing that the Court should not have reversed the decision of the Supreme Court of California. He argued that it was within their power to determine whether a contract had been breached and what damages were due as a result. Furthermore, he noted that there was no evidence presented to show any error on behalf of the court below or any misapplication of law by them in reaching their conclusion. Justice Field concluded his dissent by noting that if this case involved federal questions then they could be reviewed but since it did not involve such issues, then they should leave it alone and allow state courts to decide matters concerning contracts made under state laws without interference from federal courts.