At the outset, the AMWU expressed an ambition to replace the NSFU and ultimately to become part of the recently established Transport and General Workers Union.
In the latter instance, its effectiveness was limited by the refusal of its general secretary (Joe Cotter) to sign cheques, and the consequent impossibility of accessing union funds.
The union also lost ground at this time to the Seamen's Section of the National Minority Movement (formed 1924), which attracted many of those seafarers who were most determined to resist the reductions.
The Minority Movement, which was sponsored by the Communist Party and included black activist seafarers in this xenophobic period, was suspicious of the AMWU.
Despite the efforts of its National Organiser, Manny Shinwell, the AMWU was wound up in early 1927.