Workers at Jobcentres are among those set to take industrial action
Up to 270,000 civil servants are to stage a 48-hour strike on 8 and 9 March in a dispute over cuts to public sector redundancy terms.
The walkout will involve Jobcentre staff, tax workers, coastguards, border agency officials, courts staff and driving test examiners.
The PCS union said there could be further industrial action throughout March if the dispute is not resolved.
The government says the changes will save £500m in taxpayers' money.
Five other civil service unions have already reached agreement over the reforms, which ministers insist include "additional protection" for those public sector workers on the lowest incomes and nearing retirement.
The Public and Commercial Services 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.
Members were balloted earlier this month. The union announced that 63% had voted in favour of stoppages, with 81% backing an overtime ban.
The union says the two-day walkout could be followed by a series of rolling strikes throughout the rest of March and April - just weeks before the expected date of the general election.
General secretary Mark Serwotka said the planned reforms were "more about crude politicking than making savings".
"We have suggested ways in which the government can make these savings whilst protecting the rights of existing members, yet it seems intent on penalising the people who keep this country running," he said.
"The government needs to recognise the depth of anger which has been demonstrated by this ballot result and find the political will to negotiate a settlement that avoids a sustained campaign of industrial action."
The union's national executive committee is due to meet next week to decide on further strike dates.
Cabinet Office Minister Tessa Jowell said the new deal was "fair for staff and taxpayers".
"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," she said.
"This is, furthermore, the lowest turnout for a PCS ballot in recent years.
"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."
Ms Jowell said that plans were in place to minimise disruption to the public caused by the strike.