(law) In the United States, a person who denies the obligation to pay a tax for which the government has determined that person is liable, based on a belief that the government lacks the legal authority to impose taxes.

assertions that the imposition of the U.S. federal income tax is illegal because the Sixteenth Amendment to the United States Constitution, which reads "The Congress shall have power to lay and collect taxes on incomes, from whatever source derived, without apportionment among the several States, and without regard to any census or enumeration", was never properly ratified,Christopher S. Jackson, The Inane Gospel of Tax Protest: Resist Rendering Unto Caesar - Whatever His Demands, 32 Gonzaga Law Review 291, at 301-303 (hereinafter "Jackson, Gospel of Tax Protest").

A tax protester, in the United States, is a person who denies that he or she owes a tax based on the belief that the Constitution of the United States, statutes, or regulations do not empower the government to impose, assess or collect the tax.