The Jones Act protects American merchant mariners and ensures that American companies also employ Americans on domestic ships. It also requires that all goods shipped between ports of the United States be carried by vessels built in the United States and owned and operated by Americans. McCain is trying to slip this abolishment into the Keystone Pipeline legislation, which has absolutely nothing to do with merchant mariners. Merchant mariners are essential to the US economy and repealing the Jones Act will allow foreign merchants to come here and take the jobs of American citizens.
For more information on the Jones Act, look at these links.
http://gcaptain.com/senator-john-mccain-launches-new-attack-on-jones-act/