British Gas engineers will take part in five 24-hour strikes in the coming weeks in a battle with the company over pension rights.
It is estimated that up to 6,000 engineers will down tools on December 12th, 19th and 21st and January 6th and 9th.
In addition, out-of-hours calls will not be handled from December 12th to the 23rd, and from January 4th to the 10th.
The GMB union, which is supporting the strike action, claimed workers had no other option.
National secretary Brian Strutton said: "We have now set out our initial plans for carrying out the very clear strike mandate that our British Gas engineer members delivered.
"It is now absolutely imperative that British Gas meets with GMB to resolve this dispute."
Centrica, which owns British Gas, insists its pension scheme is one of the best available.