48 CFR §42.102

1. (a)As provided in agency procedures or interagency agreements, contracting officers may request audit services directly from the responsible audit agency cited in the Directory of Federal Contract Audit Offices. The audit request should include a suspense date and should identify any information needed by the contracting officer.
2. (b)The responsible audit agency may decline requests for services on a case-by-case basis, if resources of the audit agency are inadequate to accomplish the tasks. Declinations shall be in writing.