In Revenue Ruling 2008-29, the IRS has provided specific guidance on the proper amount of federal income tax an employer must withhold in nine different situations under the supplemental wage regulations1 that became effective January 1, 2007. Typically, states with income taxes default to following federal regulation principles for distinguishing between regular and supplemental wages. In addition to federal income tax withholdings, states also look for proper withholding on supplemental wages for state income tax purposes.
