Workers at ESB say there will be no disruption to customer supply over the Christmas period as a result of the vote in favour of industrial action.
Staff last night voted overwhelmingly in favour of industrial action in a row over their company pension scheme.
The row centres on the company's plan to pay a dividend to Government following the payment of €78m to the State earlier this year.
Unions argue that the payments are eating into the workers' pension scheme.
Brendan Ogle, secretary of the ESB group of unions, said it will be revealed on Friday if the workers plan to mount strike action.