British Gas engineers are to stage a five-day strike in the new year in a dispute over pay and conditions.
The GMB union said its members will walk out from January 7, followed by further stoppages to be announced later.
The strike will involve around 4,500 service and repair gas engineers, 600 central heating installers, 540 electrical engineers, 170 specialist business gas engineers and 1,700 smart metering engineers, said the union.
The only exceptions to the industrial action will be dealing with emergencies and problems for households with vulnerable people, according to the union.
GMB national official Justin Bowden said the actions of British Gas had “tarnished” its reputation.
“The use of fire and rehire threats has been condemned across the political spectrum and caused huge anger among this dedicated workforce.
“There’s still time for British Gas to see sense, remove the fire and rehire threats, and negotiate a fair settlement to avoid a walkout.”
Mr Bowden said workers had been “provoked” into taking industrial action.
A Centrica spokesman said: “The GMB leadership is stuck in the past, fighting against modernisation and failing to understand that customer demands are changing; customers want better appointments and we need more flexibility to deliver for them.
“If we can’t change the way we work then we can’t do this, and our customers will turn to our competitors.
“Our new terms are fair and the majority of our workforce – including thousands of GMB members – accept that we need to change.
“We now expect to see well over 75% of our colleagues to have accepted by the end of the year.
“The GMB leaderships’ mandate for strike action is very weak and their action will harm our country, our customers, and their colleagues.”