More than a quarter of a million civil servants are set to strike for two days over changes to their redundancy pay.
Up to 270,000 members of the Public and Commercial Services (PCS) union could strike, affecting job centres, tax offices, courts, ports, borders, and emergency police call centres.
The union says that civil servants will lose up to a third of their redundancy entitlements, worth thousands of pounds.
General secretary Mark Serwotka said: "There is incredible anger among hard-working public servants who are seeing their terms ripped up. The strike will show how vital these people are to the running of our society."
He continued: "The government is tearing up the contracts of low-paid civil and public servants whilst it claims it can do nothing about bankers' bonuses because of contractual obligations."
The walkout is the biggest display of industrial unrest in the public sector since 1987, and more strikes are expected.
The government said other civil service unions agreed that the changes were fair. Tessa Jowell, the Cabinet Office minister, said: "The changes to the civil service compensation scheme were agreed with five of the six civil service unions after 18 months of negotiation and consultation. These unions all agree with us that the resulting deal is fair for staff and taxpayers.
"During the negotiating process, we responded to union concerns by ensuring additional protection for lower paid staff."
She said that those earning £30,000 or less, who constitute 80 per cent of all staff, will still get between to and three years salary. Civil servants earning over £30,000 will have their redundancy pay capped at two times salary.
