McGinty v. Flannagan was a United States Supreme Court case that addressed the issue of whether a state court could enforce a contract that was made in violation of a state statute. The case involved a contract between two parties, McGinty and Flannagan, in which McGinty agreed to pay Flannagan a certain sum of money in exchange for a certain piece of property. The contract was made in violation of a state statute that prohibited the sale of the property in question. The Supreme Court held that the state court could not enforce the contract because it was made in violation of the state statute. The Court reasoned that the state statute was a valid exercise of the state's police power and that the state had the right to protect its citizens from contracts that were made in violation of the law. The Court also noted that the state had the right to protect its citizens from contracts that were made in violation of public policy. The Court's decision in McGinty v. Flannagan established that state courts could not enforce contracts that were made in violation of state statutes. This decision has been cited in numerous cases since then and has been used to support the idea that state courts should not enforce contracts that are made in violation of the law.

Justice Field delivered the dissenting opinion in McGinty v. Flannagan, arguing that the majority's decision was contrary to both law and justice. He argued that a state court had no power to issue an injunction against a federal officer for acts done under color of his office, as it would be tantamount to enjoining the United States itself. Furthermore, he stated that even if such an injunction were permissible, this case did not meet its requirements because there was no proof of any wrong or injury committed by the defendant which could justify relief from a court of equity. Justice Field concluded by stating that while courts should protect citizens from illegal acts committed by public officers acting under color of their offices, they must also guard against interference with those who are lawfully performing their duties on behalf of the government.