41 C.F.R. § 102-118.505 Must my agency send a voluntary refund to the Treasurer of the United States?
Title 41 - Public Contracts and Property Management
No, your agency may keep and use voluntary refunds submitted by a TSP, if the refund was made prior to a Notice of Overcharge issued by the GSA Audit Division.
Title 41: Public Contracts and Property Management
PART 102–118—TRANSPORTATION PAYMENT AND AUDIT
Subpart F—Claims and Appeal Procedures
General Agency Information for All Claims
§ 102-118.505 Must my agency send a voluntary refund to the Treasurer of the United States?

