In 2015, the U.S. Supreme Court recognized the fundamental right to marry in Obergefell v. Hodges. At the same time, the tax code commonly taxes married couples at a higher effective tax rate than their unmarried counterparts. We examine the constitutionality of the penalty on marriage, critically reviewing the justification for the penalty accepted in Johnson v. U.S. in 1976. Our evaluation of the tax system suggests that the marriage tax penalty violates Due Process and may violate Equal Protection and the First Amendment for some taxpayers.