2 CFR § 200.345 - Collection of amounts due.
(a) Any funds paid to the non-Federal entity in excess of the amount to which the non-Federal entity is finally determined to be entitled under the terms of the Federal award constitute a debt to the Federal Government. If not paid within 90 calendar days after demand, the Federal awarding agency may reduce the debt by:
(1) Making an administrative offset against other requests for reimbursements;
(3) Other action permitted by Federal statute.
(b) Except where otherwise provided by statutes or regulations, the Federal awarding agency will charge interest on an overdue debt in accordance with the Federal Claims Collection Standards (31 CFR parts 900 through 999). The date from which interest is computed is not extended by litigation or the filing of any form of appeal.