Two of the country's biggest rail workers' unions, including one led by left-winger Bob Crow, have started talks aimed at a merger.
The Rail, Maritime and Transport union (RMT), and Transport Salaried Staffs' Association (TSSA) said initial discussions will focus on closer working between both unions initially through a federation structure with a view to moving towards a merger.
They added that other smaller specialist unions in transport which may be thinking along similar lines would be able to join the discussions at a future date.
TSSA general secretary Gerry Doherty said: "The decision will hopefully be the start of a process designed to serve the interests of future generations of transport and travel trade workers.
"We owe an obligation to our children to leave better organisations that protect workers in the very uncertain future that they currently face."
Mr Crow, general secretary of the RMT, said it was a "historic" move, adding: "These talks will bring together two unions each with over 100 years of specialising in the transport industry in the interests of workers."