The Transport and General Workers’ Union and Amicus are planning to merge next year.

If the merger goes ahead, it would form the UK’s largest union, with over 2 million members.

A ballot of all members of the T&G and amicus will be held in February to decide whether to proceed with the plans.

It is hoped that the new union, yet to be named, will be launched on May 1.

Tony Woodley, T&G general secretary, said: "Not since 1922, when brave and visionary men and women from 14 different unions came together to form the T&G, has our union faced such a momentous choice. To stay as we are. Or to seize the future, with all its challenges and opportunities.

"The challenge of rapidly-changing capitalism hangs over us. Globalisation is doing away with the fixed reference points many of us grew up with. A united union will mean an end to divide-and-rule, and the cancer of inter-union competition which has only helped the bosses, in one sector after another. A growing union, really investing in organising, will give more power to the elbow of our shopfloor representatives everywhere.

"If this merger is about one thing, it is this: Working-class unity, the historic aim of our movement. That is why I believe that this new union, the best hope for the unity of the working class in Britain and Ireland, will become a beacon of attraction for other workers, other trade unions looking to fight back and win in the workplace."