29 C.F.R. § 4.166
The standard by which monetary wage payments are measured under the Act is the wage rate per hour. An hourly wage rate is not, however, the only unit for payment of wages that may be used for employees subject to the Act. Employees may be paid on a daily, weekly, or other time basis, or by piece or task rates, so long as the measure of work and compensation used, when translated or reduced by computation to an hourly basis each workweek, will provide a rate per hour that will fulfill the statutory requirement. Whatever system of payment is used, however, must ensure that each hour of work in performance of the contract is compensated at not less than the required minimum rate. Failure to pay for certain hours at the required rate cannot be transformed into compliance with the Act by reallocating portions of payments made for other hours which are in excess of the specified minimum.
29 C.F.R. § 4.166