19 U.S.C. § 1505

(a) Deposit of estimated duties and fees Unless the entry is subject to a periodic payment referred to in this subsection or the merchandise is entered for warehouse or transportation, or under bond, the importer of record shall deposit with the Customs Service at the time of entry, or at such later time as the Secretary may prescribe by regulation (but not later than 12 working days after entry or release) the amount of duties and fees estimated to be payable on such merchandise. As soon as a periodic payment module of the Automated Commercial Environment is developed, but no later than October 1, 2004 , the Secretary shall promulgate regulations, after testing the module, permitting a participating importer of record to deposit estimated duties and fees for entries of merchandise, other than merchandise entered for warehouse, transportation, or under bond, no later than the 15 working days following the month in which the merchandise is entered or released, whichever comes first. (b) Collection or refund of duties, fees, and interest due upon liquidation or reliquidation The Customs Service shall collect any increased or additional duties and fees due, together with interest thereon, or refund any excess moneys deposited, together with interest thereon, as determined on a liquidation or reliquidation. Duties, fees, and interest determined to be due upon liquidation or reliquidation are due 30 days after issuance of the bill for such payment. Refunds of excess moneys deposited, together with interest thereon, shall be paid within 30 days of liquidation or reliquidation. (c) Interest Interest assessed due to an underpayment of duties, fees, or interest shall accrue, at a rate determined by the Secretary, from the date the importer of record is required to deposit estimated duties, fees, and interest to the date of liquidation or reliquidation of the applicable entry or reconciliation. Interest on excess moneys deposited shall accrue, at a rate determined by the Secretary, from the date the importer of record deposits estimated duties, fees, and interest or, in a case in which a claim is made under section 1520(d) of this title , from the date on which such claim is made, to the date of liquidation or reliquidation of the applicable entry or reconciliation. The Secretary may prescribe an alternative mid-point interest accounting methodology, which may be employed by the importer, based upon aggregate data in lieu of accounting for such interest from each deposit data provided in this subsection. (d) Delinquency If duties, fees, and interest determined to be due or refunded are not paid in full within the 30-day period specified in subsection (b), any unpaid balance shall be considered delinquent and bear interest by 30-day periods, at a rate determined by the Secretary, from the date of liquidation or reliquidation until the full balance is paid. No interest shall accrue during the 30-day period in which payment is actually made.