45 CFR § 302.75 - Procedures for the imposition of late payment fees on noncustodial parents who owe overdue support.
(b) If a State opts to impose late payment fees -
(1) The late payment fee must be uniformly applied in an amount not less than 3 percent nor more than 6 percent of overdue support.
(2) The fee shall accrue as arrearages accumulate and shall not be reduced upon partial payment of arrears. The fee may be collected only after the full amount of overdue support is paid and any requirements under State law for notice to the noncustodial parent have been met.
(3) The collection of the fee must not directly or indirectly reduce the amount of current or overdue support paid to the individual to whom it is owed.
(4) The late payment fee must be imposed in cases where there has been an assignment under section 408(a)(3) of the Act or section 471(a)(17) of the Act or the IV-D agency is providing services under § 302.33 of this chapter.
(5) The State may allow fees collected to be retained by the jurisdiction making the collection.