People who miss next Tuesday's tax self-assessment deadline because of a strike by tax office staff will not be fined.
HM Revenue and Customs said it would not be issuing penalties to anyone who filed their tax return on 1 or 2 February.
Equally, those who have tax to pay will not face any interest on payments made on 1 or 2 February.
David Gauke, Exchequer Secretary to the Treasury, said: "This strike could have caused thousands of people to incur fines, so I am pleased that HMRC has taken this common-sense approach."
Up to 20,000 members of the Public and Commercial Services Union (PCS) working in call centres and inquiry offices went on strike last week in a dispute about the appointment of private companies to run call-handling trials in two contact centres, and will walk out for 24 hours next Tuesday.
A union spokesman said: "If the minister genuinely had taxpayers' interests at heart, he would call off the trials and invest in his own staff and the essential services they provide, instead of making cuts and letting in the private sector."
The action is in protest at the appointment of two private companies, Sitel and Teleperformance, to run call-handling trials in HMRC tax credit contact centres in Lillyhall in Cumbria and Bathgate in Scotland. The year-long trials are due to start next month.