https://www.dol.gov/whd/regs/compliance/whdfs15.pdf

>A compulsory charge for service, for example, 15 percent of the bill, is not a tip. Such charges are part of the employer's gross receipts. Sums distributed to employees from service charges cannot be counted as tips received, but may be used to satisfy the employer's minimum wage and overtime obligations under the FLSA. If an employee receives tips in addition to the compulsory service charge, those tips may be considered in determining whether the employee is a tipped employee and in the application of the tip credit.