More than 400 workers from His Majesty’s Revenue and Customs (HMRC) are set to go on strike for 18 days this May and June.
The Public and Commercial Services (PCS) Union warned the strikes were “likely to cause significant problems for businesses”, with 432 of its members walking out.
The members, who work as customer service advisors in Glasgow and Newcastle-upon-Tyne, will walk out on May 10-12, 15-19, 22-26, 29-31 and June 1-2.
The announcement comes amid an ongoing dispute over pay, pensions, jobs and redundancy between the PCS and the Government.
Services including HMRC’s employer helpline, Student Loans Unit and PAYE registrations are expected to be affected by the strike action.
PCS general secretary Mark Serwotka said: “Our hard-working members in HMRC are fed up with being treated with disdain by a Government that doesn’t seem to care about its own staff.
“If they did, ministers would be able to stop this strike action tomorrow by making a fair offer to help our members through the cost-of-living crisis and beyond.”