The Amalgamated Transit Union is the largest labor organization representing transit workers in the U.S. and Canada.   Founded in 1892, the ATU, today, is comprised of over 175,000 members in over 273 local unions in 46 states and nine provinces.   The ATU includes bus, subway, light rail and ferry operators, clerks, baggage handlers, mechanics and others in the urban transit, over-the-road, and school bus industries, as well as paratransit, emergency medical, clerical, and municipal workers.
Direct link to the International ATU web site.