D.C. Mun. Regs. r. 27-3342
The cost of back pay resulting from violations of applicable District law, federal labor laws, or the Civil Rights Act of 1964 where the employee was underpaid shall be allowable.
All other back pay resulting from violations of applicable District law, federal labor laws, or the Civil Rights Act of 1964 (such as when the employee was improperly discharged, discriminated against, or other circumstances for which the back pay was not additional compensation for work performed) shall not be allowable.
The cost of back pay resulting from payments to union employees for the difference in their past and current wage rates for working without a contract or labor agreement during labor management negotiations shall be allowable.
The cost of back pay to non-union employees based on results of labor-management negotiations shall be allowable only if a formal agreement or understanding exists between management and the employees concerning the payment or an established policy or practice exists and is consistently followed by the contractor.
D.C. Mun. Regs. r. 27-3342