Trucking: Payment terms, interstate commerce act, section 377

Question
Is it a law that trucking companies should be paid by customers in 7 days after delivery date of cargo or invoice date?

Answer
William, the 7 day credit limit was in the old Interstate Commerce Act.
After deregulation carriers are authorized to extend credit and set payment terms by contract or with notice to the shippers.  If no specific agreement exists the credit limit is 15 days.
http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.as...
You of course are not required to extend credit at all and may demand payment of freight charges before delivery, however this is primarily for a one shot shipment where you don't know the shipper or their ability to pay.  Most shippers will require credit as a condition of doing business with you and some will dictate extended terms which slows down your cash flow and adds to your cost of doing business.
It all comes down to a business decision of who you want to do business with and what terms can be agreed to.
Jim.