A number of jobcentres are to merge or close, affecting up to 750 jobs.
The Department for Work and Pensions said some smaller jobcentres will merge with larger ones, and others will be co-located with local government premises.
The department said it will be able to offer a more efficient service, while delivering good value for the taxpayer and saving more than £140 million a year for the next 10 years.
The Public and Commercial Services union attacked the announcement, saying more than 70 jobcentres will close.
The DWP said its plans reflect the fact that eight out of 10 claims for Jobseeker's Allowance and 99% of applications for the Universal Credit full service are now made online.
DWP buildings are used much less, with 20% of the estate currently under-utilised.
Employment Minister Damian Hinds said: "We will always make sure that people have the support they need to get into and progress within work. These changes reflect the fact that more people access their benefits online, resulting in many of our buildings being under-used.
"We're merging some offices and locating other jobcentres with local authorities to make sure that the welfare state and our employment support works for those who need it and those who pay for it."
PCS general secretary Mark Serwotka said: "While we are pleased a handful of threatened sites will now stay open, thanks to the hard work of our members, community groups and local MPs, it is utterly disgraceful that DWP is pressing ahead with these closures.
"This Tory Government is abandoning unemployed, sick and disabled people, making it harder for them to access the services they need, and putting jobcentre jobs at risk.
"We will continue to oppose these plans in every way we can."
The DWP said 68 smaller jobcentres will be merged into larger or under-used ones nearby, four will move to new sites and 40 will co-locate with local authorities or other community services.
Four offices will close, leaving almost 800 across the country.
Most staff will remain in their current offices with others moving to another site nearby, the DWP added.
Redundancies are expected to be less than 1% of the DWP's overall staff total and the majority of these will be covered by a voluntary redundancy scheme.
The PCS announced that its members in the Eastern Avenue jobcentre in Sheffield, one of the threatened sites, will strike again from July 17 to 21 following a week-long walkout in June.
Debbie Abrahams, shadow work and pensions secretary, said: "The Government is planning to force a million more working people to attend a jobcentre under its plans for in-work sanctions, while simultaneously closing one in every 10 jobcentres across the country. A decision that affects up to 750 jobs.
"This shows the flawed logic of this Government's chaotic austerity agenda.
"Either the right hand doesn't know what the left is doing under this chaotic Government, or they are both acting together to make working people's lives harder.
"It is now absolutely clear that this Tory Government has no interest in helping people to find decent and secure work."