In 2011, the U.S. Department of Labor added language to the Fair Labor Standards Act, or FSLA — which establishes minimum wage, overtime pay, recordkeeping, and youth employment standards in both government and the private sector — to ban restaurant and bar tip pooling between front-of-house workers (servers, bartenders, etc.) and non-tipped back-of-house employees (such as chefs and dishwashers).
Depending on the state, tipped employees may be paid as little as $2.13 an hour, the idea being that the balance of the applicable minimum wage is made up with tips. Untipped back-of-house staff, on the other hand, must be paid at least the regular minimum wage.
The Department of Labor instituted the 2011 rule out of concern that tip pooling would be used as an argument by employers to pay the lower minimum to all employees.