Thousands of JobCentre and benefit office workers are to hold a 48-hour strike over job cuts, the Public and Commercial Services union has said.
The government wants to redirect the cash saved by the job cuts
The walk-out on January 26-27 comes after talks broke down between the PCS and Department for Work and Pensions over the cutting of 30,000 posts.
The union said services were already being affected across the UK by the loss of 15,000 jobs since March 2004.
The government said it was disappointed the PCS has opted for strike action.
The union had appealed to the DWP to halt the cuts while an assessment is made of their impact.
Union leaders want a guarantee of no compulsory redundancies among the staff, which also includes workers in pension centres and the Child Support Agency.
PCS general secretary Mark Serwotka said: "Strike action is not a step we take lightly. But against a backdrop of the DWP refusing to acknowledge the damage being wrought by job cuts, our members will take action to defend the services they deliver.
"Unless the department wake up and halt the job cuts programme and look objectively at staffing levels, there is a real danger that some of the most disadvantaged in society will be let down and no longer get the hand-up they need."
The union claims telephone calls to JobCentres are going unanswered, while people are having to wait hours to see an adviser.
They also warned that staff were facing an increasing number of assaults because of high levels of frustration being built up by the delays.
But a spokeswoman for the Department of Work and Pensions said they had hoped to work through the plans "through discussion, not industrial action".
"If we are going to meet our commitment to deliver the highest quality of service to our customers it is vital we push ahead with our modernisation programme," she said.
"It is therefore disappointing that the PCS appear to not be moving in the same direction and seem opposed to much of the change.
"We are absolutely committed to our service to the public. Our robust contingency plans will ensure that our top priority - to make payment to our customers - is maintained."
Gordon Brown announced the redundancies in March 2004 as part of wider cuts across the civil service in order to channel cash into frontline services, such a doctors and nurses.