From the Fair Labor Standards Act, originally passed in 1973:

177.24 PAYMENT OF MINIMUM WAGES 3. No employer may require an employee to contribute or share a gratuity received by the employee with the employer or other employees or to contribute any or all of the gratuity to a fund or pool operated for the benefit of the employer or employees. ... The commissioner may require the employer to pay restitution in the amount of the gratuities diverted.