The ESB has appealed to a union representing network technicians to call off industrial action scheduled to commence tomorrow with a work-to-rule that could affect repair services during the week.

The Independent Workers Union claims to represent up to 550 of the company's 1,200 network technicians who deal with breakdowns.

However, the ESB does not recognise the IWU, and the unions that it does recognise - Connect, SIPTU and Unite - dispute those numbers, and are not participants in the industrial action.

The IWU members will commence a work-to-rule tomorrow morning at 8 am, and will refuse to do overtime, on-call, or standby duties.

They will escalate to a 24-hour strike on Friday, with a two-day stoppage in the following week.

IWU Regional Secretary Gerry Corbett said the impact of the work to rule may not emerge until after 5pm in the coming days, when the requirement for call-out or standby duties could arise.

He said the IWU was willing to discuss providing an essential emergency service, but had had no contact from the ESB about that.

The Unite trade union, which says it represents 540 network technicians, confirmed that it was not in dispute with the company.

Unite Regional Coordinating Officer Richie Browne said his members had not balloted for industrial action, and was advising staff to report for work as normal.

He said a negotiation process with the company was currently under way overseen by former Labour Court chair Kevin Duffy after staff rejected company proposals before Christmas.

However he noted that the IWU was not a party to that process as it did not have collective bargaining rights for network technicians.

SIPTU and Connect were approached for comment but have not yet responded.

The IWU says the dispute centres on the failure of the ESB to adequately consult with staff over outsourcing of certain operations - a charge denied by the company.

In a letter to the IWU yesterday, ESB Legal Officer Annelie Walsh rejects union claims that there is a legitimate trade dispute - a requirement to comply with industrial relations law.

She also accused the union of failing to follow other procedures required by law.

She disputed that proper notice of industrial action has been given, and said that the IWU has not advised the company of the identity of the employees, or their locations.

"In light of the fact that what is apparently contemplated is limited industrial action, these further details are essential in order to enable ESB to have proper notice of the action that it is facing and to make arrangements to ensure the ongoing provision of essential services in a manner that ensures the safety of ESB's employees and members of the public," she wrote.

It its response, the IWU defended its compliance with procedures and confirmed that the industrial action will proceed.