A union has accused the Department of Work and Pensions of "cynically delaying" a redundancy announcement until hours after a strike vote closed.
The Public and Commercial Services Union (PCS) said the department had launched a voluntary redundancy scheme on Tuesday for staff at 13 sites.
The PCS said hundreds of jobs are now at risk in offices across the country, including Exeter, Milton Keynes, Aberdeen and Southend-on-Sea.
It came after the union closed its civil service strike ballot over a dispute on pay, pensions and redundancies at midday on Monday.
General Secretary Mark Serwotka said: "To delay this announcement until our strike ballot has closed is the epitome of cynicism and callousness.
"We'll continue to fight these unnecessary office closures at a time when our public services are already over-stretched and we need more civil servants, not less."
Last week the new Prime Minister Rishi Sunak scrapped his predecessor Boris Johnson's plan to cut the size of the civil service by a fifth.
The Prime Minister's official spokesperson said there would still be reductions in the Civil Service - but insisted there would be no "specific target".
But Mr Serwotka said: "The Government may have binned its headline plans to scrap 91,000 jobs; it's now trying to impose them by stealth."
The result of the PCS ballot is due to be announced at noon on Thursday.
A DWP spokesperson said: “This is not a plan to reduce our headcount – where possible, colleagues in offices due to close are being offered opportunities to be redeployed to a nearby site or retrained into a new role in DWP or another government department.
“We are making every effort to fully support our staff through this process, including offering some affected staff the option of considering voluntary redundancy if they wish, but our priority is for staff to remain in the Department where they can.”
On Tuesday it also emerged that more than 70,000 lecturers and staff at 150 universities will strike for three days in November in a separate dispute over pay, working conditions and pensions as the cost-of-living crisis bites.
The University and College Union (UCU) said the strikes - on November 24, 25 and 30 - will be the biggest ever to hit UK universities and could impact 2.5 million students.
UCU general secretary Jo Grady said: "Campuses across the UK are about to experience strike action on a scale never seen before. 70,000 staff will walk out and make clear they refuse to accept falling pay, cuts to pensions and insecure employment.
"This is not a dispute about affordability - it is about choices.
"Vice-chancellors are choosing to pay themselves hundreds of thousands of pounds whilst forcing our members onto low paid and insecure contracts that leave some using foodbanks. They choose to hold billions in surpluses whilst slashing staff pensions."
