Thousands of staff could walk out in response to an attempt by the firm to push through pay cuts by threatening to fire workers, union GMB has said.
It accused Centrica, which owns British Gas, of provoking the strike, which it said would cause "massive disruption".
Centrica said it would prioritise vulnerable households and emergencies during the walkout.
In a statement, GMB national secretary 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," he said.
He also suggested that the strike would cause "massive disruption to customers in the depths of winter".
A Centrica spokeswoman said: "We've done everything we can with the GMB to avoid industrial action.
"While we've made great progress with our other unions, sadly the GMB leadership seems intent on causing disruption to customers during the coldest weekend of the year, amid a global health crisis and in the middle of a national lockdown," she said.
"We have strong contingency plans in place to ensure we will still be there for customers who really need us."
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