The Commonwealth of Massachusetts v. Mellon, Secretary of the Treasury, et al., 1922 is a landmark US Supreme Court case that established principles regarding federalism and taxpayer standing. The state of Massachusetts challenged the constitutionality of a federal law known as the Maternity Act, which provided funds to states for programs aimed at reducing maternal and infant mortality rates. They argued that this was an overreach by Congress into areas reserved to states under the Tenth Amendment. However, in its decision, the court ruled against Massachusetts stating it had no legal standing to challenge a federal law on behalf of its citizens unless it could demonstrate direct injury or impairment to its sovereignty. Furthermore, individual taxpayers also lacked standing because their interest in treasury funds was too indirect and remote; they couldn't sue simply because they disagreed with how tax money was spent by government officials.

In the dissenting opinion for Commonwealth of Massachusetts v. Mellon, Justice James Clark McReynolds argued that the federal government had overstepped its constitutional boundaries by appropriating funds to states under conditions not specified in the Constitution. He believed this was a violation of state sovereignty and an intrusion into areas reserved for state governance. Furthermore, he contended that if Congress could attach conditions to funding in one area (in this case maternal health), it could do so in any other area as well, leading to potential abuse of power and erosion of states' rights. He also disagreed with majority's view on standing; he thought Massachusetts should be allowed to sue because it was directly affected by these appropriations.