166 (October 3, 1913), enacted pursuant to Article I, section 8, clause 1 of, and the Sixteenth Amendment to, the United States Constitution, allowing a federal income tax.

The plaintiff in this case, Frank R. Brushaber, was a shareholder in the defendant Union Pacific Railroad company.

In an 8–0 decision (Justice James Clark McReynolds did not participate in the decision), the Court held, in an opinion written by Chief Justice Edward Douglass White, that the Sixteenth Amendment removes the requirement that income taxes be apportioned among the states according to population (Article I, Section 9, clause 4 of the U.S. Constitution).

The Court stated: "...there can be no dispute that there was power by virtue of the Amendment during that period to levy the tax, without apportionment, and so far as the limitations of the Constitution in other respects are concerned, the contention is not open...."[1] The Court also held that the Revenue Act does not violate the Fifth Amendment's prohibition against the government taking property without due process of law.

In Brushaber, the Court held that the Sixteenth Amendment eliminated the requirement of apportionment as it relates to "taxes on incomes, from whatever source derived."

All income taxes enacted after the Amendment have been treated as excises (they have been imposed with geographic uniformity but have not been required to be apportioned).