49 CFR §375.807

1. (a)You must present an invoice within 15 days (excluding Saturdays, Sundays, and Federal holidays) of the date of delivery of a shipment at its destination.
2. (b)The credit period must be seven days (including Saturdays, Sundays, and Federal holidays).
3. (c)You must provide in your tariffs the following four things:
   1. (1)You must automatically extend the credit period to a total of 30 calendar days for any shipper who has not paid your invoice within the 7-day period. However, for charges for impracticable operations that are not collected at delivery, you may not extend the credit period beyond 30 days after you present your invoice.
   2. (2)You will assess a service charge to each individual shipper equal to one percent of the amount of the invoice, subject to a $20 minimum charge, for the extension of the credit period. You will assess the service charge for each 30-day extension the charges go unpaid.
   3. (3)You must deny credit to any shipper who fails to pay a duly-presented invoice within the 30-day period. You may grant credit to the individual shipper when the individual shipper satisfies he/she will promptly pay all future invoices duly presented.
   4. (4)You must ensure all payments of invoices are strictly in accordance with the rules and regulations of this part for the settlement of your rates and charges.