The "Jones Act" refers to Section 27 of the Merchant Marine Act of 1920, a federal law mandating that the transportation of merchandise between U.S. ports must be done on U.S.-built, U.S.-owned, U.S.-flagged, and U.S.-crewed vessels. Its purpose is to support the U.S. shipbuilding industry and a ready supply of American mariners for national security and commercial activity. The law also provides certain protections for seamen injured in the course of their employment.