More than a million local government workers are to be balloted for strike action over planned pension changes.
Unison's Dave Prentis says the dispute is serious
Nine unions will begin the voting process within weeks unless Whitehall drops plans to alter the scheme.
Town hall workers, some teachers, probation officers and other public sector workers will be involved.
The unions who could go out include Unison, Amicus, the Transport and General Workers Union, the GMB, and the National Union of Teachers.
They said the move was in protest at planned cuts to the pension scheme.
Unison general secretary Dave Prentis warned government and council employers the dispute was serious.
The unions said the clock was ticking towards one of the biggest strikes for decades.
If ballots go ahead, results would be expected in late February.
Talks on the row have been ongoing for the past year, but union leaders today decided to threaten action in an attempt to break the deadlock.
They said local authority employers wanted to cut pension rights without protecting all workers in the scheme.
Employers wanted to scrap the so-called 85 rule - under which workers whose age and the length of their service added up together to 85 years could retire early.
It means a worker aged 60 with 25 years service did not have to wait until he was 65 to retire.
Mr Prentis said the dispute affected 1m members who had paid 6% of salary into schemes for decades but were now being told the deal was off.
"The local government employers and the Government should be in no doubt of how serious we are," he said.
"All we are asking is for members of the local government pension scheme to be treated fairly - the same way as other public sector workers."
Amicus general secretary Derek Simpson said the plans were worse than those previously presented, so it was "safe to assume" workers would vote to strike.
"Local government workers already have a worse scheme than other public sector workers and suffer extremely low pay, earning as little as £12,000 a year in stressful and physically demanding jobs at the front line of our public services," he said.
"All we are asking is for their equal treatment with other public sector groups who have had their existing pension benefits protected by the Government."
Their comments were echoed by the TGWU and the GMB.
The Fire Brigades Union will hold a special conference in Southport in February to discuss balloting firefighters for strike action in the same dispute.
Unions representing civil servants, teachers and health workers struck a deal with the Government last year over guaranteeing pensions.
Leaders of local authority workers have been trying to strike a similar agreement during talks with the employers and Deputy Prime Minister John Prescott.
A spokesman for the Office of the Deputy Prime Minister (ODPM) said the government was committed to decent and secure pensions for local government employees and they must be affordable, viable and fair to taxpayers, who guarantee their security.
It said that Mr Prescott's role was to oversee the pension scheme, to ensure its on-going solvency and viability and negotiations on the terms and meeting its costs is a key area for the unions and local government employers.
A ballot was a matter for the unions, he said, but the ODPM wanted to continue to hold meetings on changing the scheme.
Unions and employers' representatives agreed to hold meetings at a committee in November, he added.
The Local Government Association said the union announcement was "deeply disappointing", adding that council taxpayers could not afford to pay more for workers' pensions.
Chairman Sir Sandy Bruce-Lockhart, said: "Local government staff currently retire at 65, compared to the rest of the public sector at 60, and this is the best way forward.
"The employee staff contribution compared to the employer council tax contributions are currently not balanced and this must be addressed."