In the case of Graniteville Manufacturing Co. v. Query et al., 1930, the U.S Supreme Court ruled in favor of Graniteville Manufacturing Company, overturning a South Carolina state law that imposed an additional tax on companies using hydroelectric power generated outside the state. The court found this to be discriminatory and unconstitutional under both the Commerce Clause and Equal Protection Clause of the Fourteenth Amendment. The decision emphasized that states cannot impose taxes or regulations which discriminate against interstate commerce or unduly burden it, thereby reinforcing federal supremacy over interstate commerce regulation.

In the dissenting opinion for Graniteville Manufacturing Co. v. Query et al., it was argued that South Carolina's tax law, which imposed a higher tax on out-of-state corporations than in-state ones, did not violate the Equal Protection Clause of the Fourteenth Amendment. The dissenting justices believed that there were valid reasons for treating domestic and foreign corporations differently due to their different relationships with the state government and its citizens. They also disagreed with majority’s interpretation of previous case law regarding discriminatory taxation, arguing instead that those cases allowed states some leeway in taxing foreign companies at higher rates as long as they weren’t doing so arbitrarily or without reason.