ASLEF could become the latest union to disaffiliate from the Labour Party at its upcoming conference.
According to LabourList, a motion is going to the annual assembly of delegates which will propose that the train drivers’ union splits from the party.
Some 80 delegates from around 170 branches will consider the motion in Bournemouth on May 16th.
Sources within the group say it is expected to be a narrow result, with some saying there is a real risk that it could pass.
In September last year the bakers’ union disaffiliated from the Labour Party with an attack on Keir Starmer for neglecting working class “aims and hopes”.
The Labour leader was accused of launching a “factional internal war” with his changes to leadership election rules that hand more power to MPs at the expense of members.
The Bakers, Food & Allied Workers Union (BFAWU) is also protesting at Sir Keir’s refusal to back a £15 hourly minimum wage, the issue that triggered the resignation of frontbencher Andy McDonald.
In a statement, it said the decision had been taken by members “who predominantly live in what’s regarded as Labour Red Wall seats”, the crucial background at the next election.
It “shows how far the Labour Party has travelled away from the aims and hopes of working-class organisations like ours”, the statement read.
Unite has also put the party under pressure.
General secretary Sharon Graham has said the “remaining financial support” her union gives Labour is “now under review”, amid an ongoing industrial dispute.
The powerful union boss, who replaced Len McCluskey last year, has raised concerns over an industrial dispute with a Labour council – and warned Sir Keir that the party must act like “the party for workers” again.
“Let me be very clear – the remaining financial support of Labour Party is now under review,” she said in a message on Wednesday evening.
“Your behaviour and mistreatment of our members will not be accepted. It’s time to act like labour, be the party for workers.”