Andrus v. St. Louis Smelting and Refining Company was a United States Supreme Court case that addressed the issue of whether a state court could enjoin a federal court from hearing a case. The plaintiff, Andrus, had filed a suit in the federal court against the defendant, St. Louis Smelting and Refining Company, for damages resulting from the defendant's alleged negligence. The defendant then sought an injunction from the state court to prevent the federal court from hearing the case. The Supreme Court held that the state court did not have the authority to enjoin the federal court from hearing the case. The Court reasoned that the state court was not a superior court to the federal court and, therefore, did not have the power to enjoin the federal court from hearing the case. The Court further held that the state court's injunction was an unconstitutional interference with the federal court's jurisdiction. The Court concluded that the state court's injunction was void and the federal court was free to proceed with the case.

Justice Harlan delivered the dissenting opinion in Andrus v. St. Louis Smelting and Refining Company, arguing that the majority had failed to consider an important point of law: whether or not a state court could constitutionally enjoin a federal officer from performing his duties under federal law. In this case, the Supreme Court of Missouri had issued an injunction against Commissioner Andrus preventing him from collecting taxes on certain ores owned by St. Louis Smelting and Refining Company (SLSR). Justice Harlan argued that such action was unconstitutional because it interfered with Congress' power to regulate commerce among states as well as its ability to impose taxes for revenue purposes; thus, he believed that any attempt by a state court to interfere with these powers should be declared void ab initio - nullified from its inception - regardless of whether or not SLSR's claim was valid in itself. He further noted that if such interference were allowed without consequence then it would open up opportunities for other states courts to do likewise which could lead ultimately lead to chaos within our system of government due largely in part due conflicting laws between different jurisdictions throughout the country.