(U.S. maritime law) The U.S. Merchant Marine Act of 1920 and related statutes, commonly known as the Jones Act, require that vessels used to transport passengers or cargo between U.S. ports be built in U.S. shipyards, owned by U.S. citizens, and manned by U.S. crews. The purpose and argument for the Jones Act is to maintain a national shipbuilding and repair base as well as jobs and training for U.S. mariners, and to provide maritime assets in times of national emergencies. The argument against The Jones Act is that it is discriminatory and anti-competitive. As expected, from time-to-time the Jones Act becomes a hot political issue. The Jones Act is similar to cabotage laws in place in some 50 other nations around the world that protect domestic shipping and reserve immediate coastal activity for home fleets. See cabotage.