49 U.S. Code § 13708. Billing and collecting practices
A motor carrier subject to jurisdiction under subchapter I of chapter 135 shall disclose, when a document is presented or electronically transmitted for payment to the person responsible directly to the motor carrier for payment or agent of such responsible person, the actual rates, charges, or allowances for any transportation service and shall also disclose, at such time, whether and to whom any allowance or reduction in charges is made.
(b) False or Misleading Information.—
(c) Allowances for Services.—
When the actual rate, charge, or allowance is dependent upon the performance of a service by a party to the transportation arrangement, such as tendering a volume of freight over a stated period of time, the motor carrier shall indicate in any document presented for payment to the person responsible directly to the motor carrier that a reduction, allowance, or other adjustment may apply.