Members of the Public and Commercial Services union (PCS) will stage walkouts in the next three days, threatening disruption to the work of HM Revenue and Customs (HMRC) at a key time for tax-credit claims.
The union claims years of job cuts have led to backlogs, delays and the use of private debt collectors. It is campaigning against the closure of enquiry centres and the loss of 2000 jobs.
Strikes will be held across Wales and north-west England tomorrow, Scotland and the Midlands on Thursday, and London, the south-east, south-west and east of England, Yorkshire and Humberside and Northern Ireland on Friday.
PCS general secretary Mark Serwotka said HMRC's work was being "undermined by unnecessary and politically motivated cuts".
The union said the strikes were timed to coincide with the deadline for tax credit renewals and a key date for self-assessment payments.
A spokesman for HMRC said: "It is a great shame that the union is asking HMRC staff to strike, deliberately putting the livelihoods of hard-working families at risk to further an industrial dispute.
"We will do everything we can to minimise the impact on tax credits claimants."
He said people can renew tax credits online at www.gov.uk/renewtaxcredits.