The Merchant Marine Act of 1920, which is also known as the Jones Act, is a U.S. federal statute that provides for the promotion and maintenance of the American merchant marine fleet.
According to the Jones Act, all goods transported by water between U.S. ports need to be carried on U.S.-flagged ships, which were constructed in the U.S, owned by U.S. citizens, and crewed by U.S. citizens and U.S. permanent residents.
This act has been revised a number of times and the most recent revision, which happened in 2006, included recodification in the U.S. Code.
The Jones Act is also related to the cabotage term which you can see here.
World Maritime News Staff; Image: nedoc