Labour will back public sector strikes if the Government remains "unreasonable" in talks with trade unions over efforts to secure agreement over pension reforms, deputy leader Harriet Harman indicated.
Ms Harman said she still hoped a settlement could be found but accused ministers of being "contemptuous" of workers and treating the public sector as a "millstone" around the neck of the economy.
Several unions are preparing to hold ballots for strikes ahead of a day of action on November 30 with the aim of co-ordinating stoppages - an issue certain to feature prominently at the Labour conference in Liverpool.
Opposition leader Ed Miliband, who is due to arrive in the city for the annual gathering, has carefully declined to give any formal backing at this stage to the strike action planned by the unions.
The Government has criticised the decision to ballot while talks are ongoing, insisting it remains "totally committed to genuine engagement with the unions".
Ms Harman told the Daily Telegraph: "Well, I'm sure that will be Ed's view - go on with the negotiations, make the arguments, but we're not going to be on the side of the Government behaving unreasonably to people who work hard in the public sector, just because they've got an unnecessary and harsh deficit reduction plan which is also risking the economy and because they have an antipathy to the public sector.
"So we would not be on the side of the Government, definitely, if they were unreasonable and refused to come to a proper negotiated settlement."
The unions had to be careful to "keep the public onside", she said, adding: "Everyone hopes there can be a negotiated settlement.
"But the unions are pointing out that it's not that their pension schemes are unsustainable. When we were in government, we made them sustainable. It's all to pay for (cutting) that flipping deficit too far and too fast.
"You shouldn't be saying to people they can't strike if they've gone through the processes in a just cause. The Government has made it absolutely clear that they are contemptuous of the public sector. They think it's a millstone round this country's neck."