The U.S. Federal Maritime Commission released a study on July 27, 2012 on the causes and legality of the diversion of containerized cargo among U.S. ports and ports in Canada and Mexico. The study concludes, among other things, that “carriers shipping cargo through Canadian and Mexican ports violate no U.S. law, treaty, agreement, or FMC regulation.” The study also concluded that the ad valorem U.S. Harbor Maintenance Tax payable by shippers into the Harbor Maintenance Trust Fund intended to pay for port dredging is a factor in the choice of ports by shippers.