British Gas workers have voted heavily in favour of strikes in a dispute over pay and conditions.
The GMB union said its members backed industrial action by almost 9 to 1.
Officials will meet in the coming days to consider strike dates, threatening action by British Gas engineers over the festive season.
GMB national officer Justin Bowden said: “The ultimatum from British Gas to its workforce to accept these cuts before Christmas or get the sack has now made strike action unavoidable.
“Our members had already voted in huge numbers to reject the company’s draconian cuts to terms and conditions.
“GMB shop stewards and officials will meet to consider and assess the ballot result and the nature of the industrial action and the dates for action – initially across January.
“They will also consider what emergency cover is required, including for the elderly and vulnerable households.”
Mr Bowden said British Gas and parent company Centrica were “entirely to blame” for any disruption by “provoking” workers into strike action with threats and deadlines to either accept substantial cuts in pay and conditions or be sacked.
A spokesman for Centrica said: “Only 52% of the eligible GMB membership has voted to support strike action. This is a very weak mandate.
“It is clear the GMB leadership does not have popular support across their membership for this course of action.”
A Centrica spokesman added: “We now expect to see well over 75% of colleagues accepting the changes by the end of the year.
“We believe the majority understand that change is critical in making our business more sustainable and competitive and this will help protect well-paid and highly skilled jobs for the long term.
“The GMB leadership’s mandate for strike action is weak and it’s disappointing that they would take such wrong-headed and cold-hearted action during winter and amid a global health crisis.
“We have strong plans in place to mitigate any disruption caused by a strike and we will do everything we can to be there for our customers – particularly those who are vulnerable or have emergencies.
“GMB’s actions have the potential to cause our customers harm when they need us most and we call on them to reconsider as it’s not too late to do the right thing for our colleagues, for our customers, and for our country.”