29 CFR § 778.310 - Fixed sum for varying amounts of overtime.
A premium in the form of a lump sum which is paid for work performed during overtime hours without regard to the number of overtime hours worked does not qualify as an overtime premium even though the amount of money may be equal to or greater than the sum owed on a per hour basis. For example, an agreement that provides for the payment of a flat sum of $75 to employees who work on Sunday does not provide a premium which will qualify as an overtime premium, even though the employee's straight time rate is $5 an hour and the employee always works less than 10 hours on Sunday. Likewise, where an agreement provides for the payment for work on Sunday of either the flat sum of $75 or time and one-half the employee's regular rate for all hours worked on Sunday, whichever is greater, the $75 guaranteed payment is not an overtime premium. The reason for this is clear. If the rule were otherwise, an employer desiring to pay an employee a fixed salary regardless of the number of hours worked in excess of the applicable maximum hours standard could merely label as overtime pay a fixed portion of such salary sufficient to take care of compensation for the maximum number of hours that would be worked. The Congressional purpose to effectuate a maximum hours standard by placing a penalty upon the performance of excessive overtime work would thus be defeated. For this reason, where extra compensation is paid in the form of a lump sum for work performed in overtime hours, it must be included in the regular rate and may not be credited against statutory overtime compensation due.