The country's biggest union will today discuss calls for Labour to reconsider its approach to a referendum on the European Union amid warnings that its current policy could be an "electoral millstone".
Unite will debate Britain's relationship with Europe at its national conference in Liverpool, with the union believing the country is better off in the EU.
But a statement from Unite's executive said austerity policies from the European Commission had imposed suffering on countries including Ireland, Greece and Spain, while mass unemployment had been "imposed" on eurozone countries.
"A policy which combines uncritical support for the present working of the European Union while denying any opportunity for a referendum on Britain's membership is thus likely to be an electoral millstone for Labour at the general election.
"Conference calls on the Labour leadership to urgently reconsider its approach to the question of a referendum on Britain's membership of the EU, on the grounds that this issue can never be resolved except on the basis of a clear democratic mandate," said the statement.
The executive said Unite will argue for a vote for Britain to stay in the EU, while campaigning against the neo-liberal agenda in Brussels.
Labour has said it will hold a referendum if additional powers are transferred from Westminster to Brussels over the course of the next Parliament, although the party does not expect that to happen.
The Conservatives will renegotiate Britain's terms of membership if they win an outright majority in next year's general election, and hold a referendum in 2017.