43 CFR §2.53

1. (a)The bureau may charge interest on any unpaid bill starting on the 31st day following the billing date.
2. (b)The bureau will assess interest charges at the rate provided in 31 U.S.C. 3717 and implementing regulations and interest will accrue from the billing date until the bureau receives payment.
3. (c)The bureau will follow the provisions of the Debt Collection Act of 1982 (Public Law 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.
4. (d)This section does not apply if you are a state, local, or tribal government.