26 C.F.R. § 31.3401(a)(16)-1
Tips paid to an employee are excepted from wages and hence not subject to withholding if-
However, if the cash tips received by an employee in a calendar month in the course of his employment by an employer amount to $20 or more, none of the cash tips received by the employee in such calendar month are excepted from wages under this section. The cash tips to which this section applies include checks and other monetary media of exchange. Tips received by an employee in any medium other than cash, such as passes, tickets, or other goods or commodities do not constitute wages. If an employee in any calendar month performs services for two or more employers and receives tips in the course of his employment by each employer, the $20 test is to be applied separately with respect to the cash tips received by the employee in respect of his services for each employer and not to the total cash tips received by the employee during the month. As to the time tips are deemed paid, see § 31.3401(f)-1 . For provisions relating to the treatment of tips received by an employee prior to 1966, see paragraph (b)(11) of § 31.3401(a)-1 .
26 C.F.R. §31.3401(a)(16)-1