HM Revenue and Customs is planning to close 137 offices under a modernisation programme.
A total of 13 new regional centres will be opened over the next five years.
The Public and Commercial Services (PCS) union said the cuts would pose a “significant threat” to the operation of HMRC as well as to the working lives of staff.
The union called for full public and parliamentary scrutiny of the decision.
HMRC said its modernisation programme includes investment in new online and other services to make it easier for people to pay their tax.
Lin Homer, HMRC’s chief executive, said: “HMRC is committed to modern, regional centres serving every region and nation in the UK, with skilled and varied jobs and development opportunities, while also ensuring jobs are spread throughout the UK and not concentrated in the capital.
“HMRC has too many expensive, isolated and outdated offices. This makes it difficult for us to collaborate, modernise our ways of working, and make the changes we need to transform our service to customers and clamp down further on the minority who try to cheat the system.
“The new regional centres will bring our staff together in more modern and cost-effective buildings in areas with lower rents.
“They will also make a big contribution to the cities where they are based, providing high-quality, skilled jobs and supporting the Government’s commitment for a national recovery that benefits all parts of the UK.”
HMRC said the majority of staff will move to the new regional centres.
There are around 58,000 employees spread over 170 offices across the country, ranging in size from 6,000 staff to fewer than 10.
Employees will be brought together in 13 large regional centres, with moves phased in over 10 years to minimise redundancies.
PCS general secretary Mark Serwotka said: “No-one should be in any doubt that, if implemented, these proposals would be absolutely devastating for HMRC and the people who work there.
“Closing this many offices would pose a significant threat to the operation of HMRC, its service to the public and the working lives of staff, and the need for parliamentary scrutiny of the plans is undeniable and urgent.”