A senior union leader has called for an emergency meeting of the TUC to plan a campaign of industrial and political action against expected cuts in the pay and pensions of public sector workers.
Bob Crow, general secretary of the Rail Maritime and Transport union, said he feared the coalition Government was planning to hit pay, jobs and pensions in the public sector as part of cuts expected to be announced in Tuesday's Budget.
Prime Minister David Cameron said it was "fair" that public sector workers should face a pay and pensions squeeze in the emergency Budget.
Along with the bill for welfare payments, they were the three major areas of spending "that you can't ignore" in trying to find the significant savings needed to tackle the record £155 billion deficit, he said.
Mr Crow reacted angrily to a weekend newspaper interview given by Mr Cameron in which he insisted there was no agenda against public sector workers despite the need to make savings.
Mr Crow said: "David Cameron has launched a full-frontal assault on the trade union movement on a scale which is unprecedented since Margaret Thatcher's government set out to smash the National Union of Mineworkers. It could not be clearer that the ConDem administration are setting out to drive down pay, working conditions and pensions.
"When someone's winding up to give you a kicking you have a clear choice - you can either take them on right from the off or you can roll over and hope that they go away.
"RMT is calling on the trade union movement to start the fight-back right here, right now before Cameron and Clegg have had a chance to pull their boots on.
"This is not the time for talking, it's the time for action. We need an emergency meeting of the Trade Union Congress to co-ordinate the political and industrial action that we will need to take as a united movement to drive back the ConDem attack on our members."
Mr Crow also criticised the decision to invite Mr Cameron to address this year's TUC Congress in Manchester in September, pledging to lead a walkout of delegates.