HM Revenue & Customs (HMRC) said it will not be issuing penalties to anyone who files a return on 1 or 2 February.
Those who have tax to pay will not face any interest on payments made those dates.
Stephen Banyard, HMRC’s acting director general of personal tax, said: “We’ve always been very clear that we want the returns – not the penalties. We don’t want anyone who can’t get through for help and advice on January 31 to be disadvantaged in any way.”
David Gauke, exchequer secretary to the Treasury, said: “This strike could have caused thousands to incur fines, so I am pleased that HMRC has taken this commonsense approach.”