The Public and Commercial Services (PCS) Union said 432 of its members working as customer service advisers 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 came amid a dispute over pay, pensions, jobs and redundancy between the PCS and the government.
The union predicts the walkouts will cause “significant problems” for businesses across the UK, with services including HMRC’s employer helpline, Student Loans Unit and PAYE registrations set to be affected.
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.”
It comes as the UK has been rocked by months of industrial action from rail service workers, NHS staff, teachers, and others.
Cabinet ministers including Health Secretary Steve Barclay and former Transport Secretary Grant Shapps are among those who have come under fire for their handling of the ongoing disputes.
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know