The ESB has accused the ATGWU of breaching process in a dispute over the employment of outside contractors at the state company.
The ESB said it is "very concerned" at a threat by network technicians to go on strike from next Monday over the role of outside contractors. It described the threat as "totally unwarranted".
The dispute is over the extent to which outside contractors are involved in the delivery of a €3.6 billion programme to upgrade and modernise the company's network.
Some 1,700 external contractors are employed by ESB Networks alongside some 2,200 staff technicians, more than half of whom are represented by the ATGWU.
The ATGWU says a number of ESB apprentices are unable to secure jobs with the company because of the extent to which outside contractors are being used. Its members balloted last month in favour of industrial action.
