Staff at ESB have voted for industrial action in a row over their company pension scheme.
Workers voted by a margin of seven-to-one to take action over plans to pay a major dividend to the government.
ESB paid a dividend of €78m to the State earlier this year - a move which workers said was in breach of a previous deal.
They say the company should instead be putting the money into the company pension scheme, which has a deficit of around €1.5bn.
Unions will decide later this week what form the industrial action should take.
ESB, which has already put €591m into the scheme, stated that it is disappointed with the outcome.