29 CFR 547.2: Disqualifying provisions.

(a) No employee's participation in the plan shall be on other than a voluntary basis.

(b) No employee's wages or salary shall be dependent upon or influenced by the existence of such thrift or savings plan or the employer's contributions thereto.

(c) The amounts any employee may save under the plan, or the amounts paid by the employer under the plan may not be based upon the employee's hours of work, production or efficiency.