49 C.F.R. § 377.209 Additional charges.
Title 49 - Transportation
When a carrier— (a) Has collected the amount of tariff charges represented in a freight bill presented by it as the total amount of such charges, and (b) Thereafter presents to the shipper another freight bill for additional charges— the carrier may extend credit in the amount of such additional charges for a period of 30 calendar days from the date of the presentation of the freight bill for the additional charges.
Title 49: Transportation
PART 377—PAYMENT OF TRANSPORTATION CHARGES
Subpart B—Extension of Credit to Shippers by Motor Common Carriers, Water Common Carriers, and Household Goods Freight Forwarders
§ 377.209 Additional charges.

