Fourteenth Amendment, Section 1:
All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.
When no other remedy is available, due process is denied by a judgment of a state court withholding a decree in equity to enjoin collection of a discriminatory tax. 1 Requirements of due process are similarly violated by a statute that limits a taxpayer’s right to challenge an assessment to cases of fraud or corruption, 2 and by a state tribunal that prevents the recovery of taxes imposed in violation of the Constitution and laws of the United States by invoking a state law that allows suits to recover taxes alleged to have been assessed illegally only if the taxes had been paid at the time and in the manner provided by such law. 3 In the case of a tax held unconstitutional as a discrimination against interstate commerce and not invalidated in its entirety, the state has several alternatives for equalizing incidence of the tax: it may pay a refund equal to the difference between the tax paid and the tax that would have been due under rates afforded to in-state competitors; it may assess and collect back taxes from those competitors; or it may combine the two approaches. 4