29 C.F.R. § 20.61 – Waiver.

(a) The Department of Labor agency responsible for collecting the claim shall waive the collection of interest on the debt or any portion of the debt which is paid within 30 days after the date on which interest began to accrue. This 30-day period may be extended for another 30 days on a case-by-case basis, if the agency reasonably determines that such action is appropriate, and is in accordance with these regulations. Also, the responsible agency may waive charges assessed under this subpart, based on criteria specified in the Federal Claims Collection Standards relating to the compromise of claims (without regard to the amount of the debt), or if the agency determines that collection of these charges would be against equity and good conscience or not be in the best interests of the United States. Waiver under the first sentence of this paragraph is mandatory. Under the second and third sentences waiver is permissive and may be exercised only in accordance with the standards set by these regulations.
(b) Agencies may waive interest and other charges under appropriate circumstances, including, for example:
1. (1) Pending consideration of a request for reconsideration, administrative review, or waiver under a permissive statute,
2. (2) If the agency has accepted an installment plan, there is no fault or lack of good faith on the part of the debtor, and the amount of interest is large enough in relation to the size of the debt and the amount of the installments that the debtor can reasonably afford to pay so that the debt can never be repaid, or
3. (3) If repayment of the full amount of the debt is made after the date upon which interest and other charges became payable and the estimated costs of recovering the residual interest balance exceed the amount owed the Agency.
(c) Where a mandatory waiver or review statute applies, interest and related charges may not be assessed for those periods during which collection action must be suspended.