49 CFR §375.217

1. (a)You must specify the form of payment when you prepare the estimate. You and your agents must honor the form of payment at delivery, except when a shipper agrees to a change in writing.
2. (b)You must specify the same form of payment provided in paragraph (a) of this section when you prepare the bill of lading.
3. (c)Charge or credit card payments:
   1. (1)If you agree to accept payment by charge or credit card, you must arrange with the individual shipper for the delivery only at a time when you can obtain authorization for the shipper's credit card transaction.
   2. (2)Paragraph (c)(1) of this section does not apply to you when you have equipped your motor vehicle(s) to process card transactions.
4. (d)You may maintain a tariff setting forth nondiscriminatory rules governing collect-on-delivery service and the collection of collect-on-delivery funds.
5. (e)If an individual shipper pays you at least 110 percent of the approximate costs of a non-binding estimate on a collect-on-delivery shipment, you must relinquish possession of the shipment at the time of delivery.