The U.S. Supreme Court case Brushaber v. Union Pacific Railroad Company in 1915 was a landmark decision that upheld the constitutionality of the federal income tax. Frank R. Brushaber, a shareholder in the Union Pacific Railroad, argued that the recently enacted Federal Income Tax Law of 1913 violated constitutional limitations on direct taxation because it did not apportion taxes among states based on population as required by Article I, Section 2 and Section 9 of the Constitution. The court rejected this argument with Chief Justice White ruling that income taxes are indirect taxes which do not need to be apportioned among states according to their populations but can be levied uniformly across all taxpayers regardless of where they live or earn their incomes.

The dissenting opinion in the Brushaber v. Union Pacific Railroad Company case argued that the Sixteenth Amendment did not grant Congress new taxing powers, but merely removed the requirement for direct taxes to be apportioned among states based on population. The justices contended that income tax was still a direct tax and thus unconstitutional unless apportioned. They believed that this interpretation of the amendment would lead to an unfair distribution of taxation burden, as wealthier states could potentially bear more than their fair share due to higher incomes. Furthermore, they expressed concern about potential abuses of power by Congress if given unrestricted authority over income taxation without any constitutional limitations or safeguards against arbitrary and oppressive legislation.