One of the UK's biggest trade unions says pension reform plans could trigger the biggest wave of industrial action since the General Strike in the 1920s.
Unison leader Dave Prentis said unions were prepared for "sustained and indefinite" strikes over proposed changes to public sector pensions.
The TUC - the Trades Union Congress - said Mr Prentis was reflecting "real anger" across the union movement.
But Business Secretary Vince Cable said most trade unions wanted to negotiate.
"It's a very complex, difficult issue but there's got to be reform otherwise the burden falls on taxpayers and future generations," he said.
"We have to do something about it and it has to be done through constructive negotiation and I think that's where most trade unionists want to be."
'War of words'
Chief Secretary of the Treasury, Danny Alexander, said unions would make a "colossal mistake" if they rejected the coalition government's plan.
Mr Prentis told The Guardian he still hoped to negotiate a settlement.
The BBC's political correspondent Ben Wright said: "Privately, talks are continuing between the trade unions and the Treasury about the government's proposals but publicly the two sides are locked in a war of words."
The government wants to reform public sector pensions - meaning a later retirement age and higher contributions for most workers - and claims the current pension system is unaffordable in the long-term.
Mr Alexander said the government was proposing public sector workers - bar the armed forces, police and fire service - would receive their occupational pension at the same time as the state pension in future.
Many can currently receive a full pension at 60. The state pension age is due to rise to 66 for both men and women by April 2020.
Teachers' unions in England and Wales have already voted to strike on 30 June to protect their pensions. They will walk out on the same day as PCS union members, who are mainly from the civil service and government agencies.
The strike by the National Union of Teachers (NUT) and the Association of Teachers and Lecturers (ATL) is expected to disrupt thousands of schools.
General secretary of the ATL, Dr Mary Bousted, warned it would be more costly in the long run for the government not to work out a proper settlement.
She urged the government to "take the diktat about increased pension contributions off the table, come to the table and negotiate about everything in good faith".
"Let's find a solution which means that teachers when they retire don't have to live off means-tested benefit, which will cost the state more," she said.
Unison's 1.3 million members, who work for local authorities, the NHS, colleges and the police, have not yet been balloted on industrial action.
Mr Prentis said if strikes did happen they would be the biggest since the General Strike of 1926 and, unlike the miners' strike in 1984/5, the unions would win.
Public sector workers are already facing heavy job cuts and a pay freeze.
Mr Prentis said: "I strongly believe that one day of industrial action will not change anyone's mind in government... we are prepared for rolling action over an indefinite period."
He also called on the Labour Party to support Unison's battle against the pension reforms.
Mr Prentis, whose union is affiliated to Labour, said: "We want our Labour Party to be the voice of opposition. We're worried that some of the senior people in the party still have to make statements as if they are in power, not opposition.
"If the Labour Party stays quiet that will be an issue," he added.
Brendan Barber, TUC general secretary, said, like Mr Prentis and Dr Bousted, he wanted to see the matter resolved by negotiation with the government.
If not, he said, he believed there would be "very strong, broad public support" for industrial action, even if strikes were widespread.
"I don't think the wider public actually see their public service colleagues in the way that some people like to portray them... as the kind of parasites some media commentators present," he told the BBC's Today programme.