The secretary of the ESB Group of Unions has said there is the possibility of a disruption to service this winter after staff yesterday voted to take industrial action in a row over a €1.6bn deficit in the company pension scheme.
However, Brendan Ogle said he could not say how damaging the action would be to customers or how long it would last.
Mr Ogle said action to be taken by staff will be discussed on Friday.
He said talks aimed at resolving the pension crisis had been ongoing for two-and-a-half years.
The action was about protecting pension rights and was not about wages, he said.
Workers oppose the company's decision to pay a dividend of €78m to the State during the summer while the pension deficit remains outstanding.
The company is also expected to pay a special dividend of €400m to the Exchequer following the sale of certain assets.
87.5% of those balloted backed industrial action, with 12.5% against, with a turnout of 81%.
Arriving for a Cabinet meeting this morning, Minister for Public Expenditure and Reform Brendan Howlin said that any threat to the security of the energy supply was a matter for concern.
He said any dispute would have an impact on recovery, the economy and job creation.