The Seafarers International Union, Atlantic, Gulf, Lakes and Inland Waters, AFL-CIO, represents professional United States merchant mariners sailing aboard U.S.-flag vessels in the deep sea, Great Lakes and inland trades. SIU members sail in the three shipboard departments: deck, engine and steward. They work aboard a wide variety of vessels, including commercial containerships and tankers, military support ships, tugboats and barges, passenger ships, gaming vessels and many more.