Moore v. Greenhow, Treasurer was a United States Supreme Court case that addressed the issue of whether a state could tax the income of a non-resident. The case was brought by a resident of the District of Columbia, who was employed by the United States government and received a salary from the federal government. The state of Virginia attempted to tax the income of the plaintiff, claiming that it was taxable under the state's laws. The Supreme Court held that the state of Virginia could not tax the income of a non-resident. The Court reasoned that the power to tax income was a power reserved to the federal government, and that the state of Virginia could not exercise that power. The Court further held that the state of Virginia could not tax the income of a non-resident, even if the income was earned within the state. The Court's decision in Moore v. Greenhow, Treasurer was an important victory for the federal government, as it established the principle that the federal government has exclusive authority to tax the income of non-residents. This decision has been cited in numerous subsequent cases, and has been used to support the principle that the federal government has exclusive authority to tax the income of non-residents.

In Moore v. Greenhow, Treasurer, the Supreme Court was tasked with determining whether a Virginia statute that allowed for the taxation of certain bonds issued by the state violated Article I, Section 10 of the United States Constitution. The majority opinion held that it did not violate this clause and thus upheld the tax imposed on these bonds. Justice Field dissented from this decision arguing that such a tax would be an unconstitutional burden on interstate commerce as it would discourage individuals from investing in out-of-state securities due to their increased cost relative to those within Virginia's borders. He further argued that since Congress had not granted permission for such taxes under its power to regulate interstate commerce, they should be considered invalid according to Article I, Section 10 of the Constitution which prohibits states from passing laws “impairing” or burdening interstate trade without Congressional approval.