32 C.F.R. § 37.630
In accordance with the general policy in § 37.605 , you must require a for-profit participant that has Federally approved indirect cost rates for its Federal procurement contracts to use those rates to accumulate and report costs under an expenditure-based TIA. This includes both provisional and final rates that are approved up until the time that the TIA is closed out. You may grant an exception from this requirement if there are programmatic or business reasons to do otherwise (e.g., the participant offers you a lower rate). If you grant an exception, the participant must accumulate and report the costs using an accounting system and practices that it uses for other customers (e.g., its commercial customers). Also, you must document the reason for the exception in your award file.
32 C.F.R. §37.630