The country could face power cuts in the run-up to Christmas after the ESB Group of Unions announced it will serve notice of industrial action on the company next week in a row over a deficit in the company's pension scheme.
If no resolution is found in the meantime, industrial action could take effect from 16 December.
The ESB said it had received a notification from the Group of Unions and was considering it.
This dispute centres on a €1.6bn deficit in the ESB pension scheme.
Unions believe the company carries responsibility for plugging that hole.
However, the company argues that following a major restructuring in 2010, it has no further responsibility.
Over 87% of staff have backed industrial action on the issue.
Today the group of unions has asked each of the five affiliated unions to serve individual notice of industrial action from Friday, 29 November, though they haven't indicated what form that action will take.
That notice will expire on Monday, 16 December.
In the meantime, they have accepted a management invitation to talks - giving the two sides around three weeks to come up with a solution.
Secretary of the Group of Unions Brendan Ogle said they would to avoid industrial action, but warned that given the strength of the ballot and the nature of the jobs involved, it was hard to see how there would not be a threat of disruption to power.
The ESB said it received a communication from the Unions, and was considering it.
