The Jobcentre Plus office in Cannock is among a number of centres to be closed with the loss of 2,400 jobs, staff have been told.
The Public and Commercial Services union said 17 benefit-processing sites and five contact centres will be shut, mainly over the next year, at a time of rising unemployment.
The union attacked the announcement as "deeply flawed and dangerous" and said it would remove vital support for the unemployed.
The union said the closures were coming at a time when hundreds of thousands of public sector workers were losing their jobs as a result of the Government's spending cuts.
Jobcentre Plus has already axed more than 10,000 jobs since 2009, said the union, warning that the latest losses will lead to further delays in processing claims.
PCS general secretary Mark Serwotka said: "This is a deeply flawed and dangerous plan that will remove vital support to jobseekers and people claiming welfare at precisely the time the Government's ideological cuts will throw more people out of work.
"Instead of cutting jobs, the Government should be investing in public services like these to help get people back to work more quickly and help our economy to get back on track."
The union's annual conference next week is set to launch a campaign against spending cuts, including jobcentre closures. Delegates are expected to agree to hold a ballot for nationwide industrial action by civil servants, which could be co-ordinated with other groups of public sector workers, including teachers.
The PCS said it had been told that offices earmarked for closure were at Arbroath, Ayr, Broadstairs, Caerphilly, Cannock, Carlisle, Castleford, Chester, Clydebank, Exeter, Grimsby, Halifax, Hartlepool, Huyton (Merseyside), Lincoln, Liverpool John Moores, Luton, Mansfield, Preston, Sutton in Ashfield, Totton (Southampton) and Yeovil.
A Department for Work and Pensions spokesman said: "We can't afford to carry on paying for buildings which aren't fully used.
"Frontline Jobcentre Plus services aren't impacted by this and we've made sure that all the staff affected have the option of moving elsewhere in the organisation. In tough financial times, we have to operate as efficiently as possible."