45 C.F.R. § 2105.51 – How will the Agency collect fees owed?

(a) The Agency may charge interest on any unpaid bill starting on the 31st day following the billing date.
(b) The Agency will assess interest charges at the rate provided in 31 U.S.C. 3717 and interest will accrue from the billing date until the Agency receives payment.
(c) The Agency will follow the provisions of the Debt Collection Act of 1982 (Pub. L. 97-365, 96 Stat. 1749), as amended, and its administrative procedures, including the use of consumer reporting agencies, collection agencies, and offset to collect overdue amounts and interest.
(d) This section does not apply if you are a state, local, or tribal government.