29 C.F.R. § 4.185

The records which a contractor or subcontractor is required to keep concerning employment of employees subject to the Act are specified in § 4.6(g) of subpart A of this part. They are required to be maintained for 3 years from the completion of the work, and must be made available for inspection and transcription by authorized representatives of the Administrator. Such records must be kept for each service employee performing work under the contract, for each workweek during the performance of the contract. If the required records are not separately kept for the service employees performing on the contract, it will be presumed, in the absence of affirmative proof to the contrary, that all service employees in the department or establishment where the contract was performed were engaged in covered work during the period of performance. (See § 4.179.)