31 U.S.C § 3902 (a-c)

(a) Under regulations prescribed under section 3903 of this title, the head of an agency acquiring property or service from a business concern, who does not pay the concern for each complete delivered item of property or service by the required payment date, shall pay an interest penalty to the concern on the amount of the payment due. The interest shall be computed at the rate of interest established by the Secretary of the Treasury, and published in the Federal Register, for interest payments under section 7109(a)(1) and (b) of title 41, which is in effect at the time the agency accrues the obligation to pay a late payment interest penalty.

(b) The interest penalty shall be paid for the period beginning on the day after the required payment date and ending on the date on which payment is made.

(c)

(1) A business concern shall be entitled to an interest penalty of $1.00 or more which is owed such business concern under this section, and such penalty shall be paid without regard to whether the business concern has requested payment of such penalty.

(2) Each payment subject to this chapter for which a late payment interest penalty is required to be paid shall be accompanied by a notice stating the amount of the interest penalty included in such payment and the rate by which, and period for which, such penalty was computed.

(3) If a business concern—

(A) is owed an interest penalty by an agency;

(B) is not paid the interest penalty in a payment made to the business concern by the agency on or after the date on which the interest penalty becomes due;

(C) is not paid the interest penalty by the agency within 10 days after the date on which such payment is made; and

(D) makes a written demand, not later than 40 days after the date on which such payment is made, that the agency pay such a penalty, such business concern shall be entitled to an amount equal to the sum of the late payment interest penalty to which the contractor is entitled and an additional penalty equal to a percentage of such late payment interest penalty specified by regulation by the Director of the Office of Management and Budget, subject to such maximum as may be specified in such regulations.