U.S. Department of Labor
Employment Standards Administration
Wage and Hour Division
(Revised July 2008)
Requirements
If an employer elects to use the tip credit provision the employer must allow the tipped employee to retain all tips, whether or not the employer elects to take a tip credit for tips received, except to the extent the employee participates in a valid tip pooling arrangement.
Retention of Tips: The law forbids any arrangement between the employer and the tipped employee whereby any part of the tip received becomes the property of the employer. A tip is the sole property of the tipped employee. Where an employer does not strictly observe the tip credit provisions of the Act, no tip credit may be claimed and the employees are entitled to receive the full cash minimum wage, in addition to retaining tips they may\should have received.
Service Charges: 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. Where service charges are imposed and the employee receives no tips, the employer must pay the entire minimum wage and overtime required by the Act.
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As an interesting note, if a tip is charged to a credit card the employer may withhold a percentage of the tip comparable to the percentage he pays the credit card company--as long as it does not reduce the employee's wage below the required minimum. That's a good reason to leave tips in cash.