Up to 270,000 civil servants are to stage a national two-day strike in a dispute over redundancy pay.
The walkout, on 8 and 9 March, will involve Jobcentre staff, tax workers, coastguards, border agency officials, courts staff and driving test examiners.
There could be further industrial action throughout March if the dispute is not resolved, the Public and Commercial Services Union says.
The action is the latest development in an long-running row over changes to the civil service compensation scheme, which the Government has said will save £500m in taxpayers' money.
The union complained that changes to redundancy and compensation arrangements will cost staff up to a third of their entitlements. Civil and public servants could lose tens of thousands of pounds if they are "forced" out of a job. The PCS union leaders say the cuts, planned for April, are illegal.
They say an employee with 20 years' service on an annual salary of £24,000 could lose £20,000 as a result of new caps on pay-offs to those laid-off and taking voluntary redundancy.
Ministers insist the new measures include "substantial protection" for public sector workers on the lowest incomes and those nearing retirement.
Five other civil service unions have already reached agreement over the reforms but the PCS is the largest.
In total, 63 per cent of PCS members voted in favour of stoppages and 81 per cent backed a ban on working overtime.
The union's national executive committee will meet next week to finalise further strike dates, which could be a series of rolling strikes throughout the rest of March and April – designed to cause maximum embarrassment just weeks before the expected date of the general election.
General secretary, Mark Serwotka, said: "These cuts, which will see loyal civil and public servants lose tens of thousands of pounds if they are forced out of a job, are more about crude politicking than making savings.
"We have suggested ways in which the Government can make these savings while protecting the rights of existing members, yet it seems intent on penalising the people who keep this country running.
"With civil and public service jobs increasingly at risk, this is a cynical attempt to cut jobs on the cheap which will ultimately damage the services we all rely on.
"The Government needs to recognise the depth of anger which has been demonstrated by this result and find the political will to negotiate a settlement that avoids a sustained campaign of industrial action."
The current scheme can involve a pay-off of up to three years' wages, and ministers have argued it has been overly generous and needs to be brought into line with the rest of the public sector and closer to the private sector.
Cabinet Office Minister Tessa Jowell said the new deal was "fair for staff and taxpayers".
She said: "It is very disappointing that the PCS has decided to take industrial action, especially given that less than one in five of their own members voted in favour of strike action, and that, overall, this figure represents only around 10 per cent of the total Civil Service workforce.
"The public will find it difficult to understand the PCS continuing to protest on their own against a package which brings the Civil Service into line with the rest of the public sector and still offers more generous terms than much of the private sector."
The proposals ensure that those earning £30,000 or less – 80 per cent of all staff – will still received between two and three years' salary if made redundant. Higher earning civil servants will have redundancy pay capped at two times their salary.
Head of the civil service, Sir Gus O'Donnell, said at the time of the ballot that the proposals were "fair for civil servants and affordable for the taxpayer".
He added that the pursuit of industrial action was "wholly misguided".Reuse content