A strike by 1,200 ESB technicians looks likely to go ahead next week after a meeting between management and the ATGWU ended without agreement.
The strike is due to take place on Tuesday and although the company says power supplies will not be affected, there could be delays in repairing local breakdowns.
The strike was originally planned for Monday but has been postponed by 24 hours to allow union representatives to attend a meeting with management.
The dispute centres on the company's use of external contractors.
Three years ago, ESB unions agreed to allow the company to engage 1,700 external contractors to carry out upgrading work on its system.
However, the ATGWU now claims that the company is now relying excessively on the external staff and says that 50 apprentices will be let go at the end of their training as a result.
The ESB has denied the ATGWU's claims, pointing out that apprentices have never had any guarantee of continuing employment after their training.
It has also accused the union of breaching internal procedures.
A second union at the company, the TEEU, has instructed its members to report for work as normal next week regardless of whether the ATGWU places pickets at company premises.
The TEEU said it was concerned that the planned strike would compromise the future of the remaining apprentices.
Leaving today's meeting, ATGWU Official Brendan Ogle said that ESB management had put nothing new on the table. He said that no further talks are scheduled but that his union will be issuing a statement this evening.
Asked about the TEEU position, Mr Ogle said that he had always been opposed to anti trade union Thatcher practices.
He said he was disappointed that the Irish trade union movement had sunk so low as to invite members to offer black leg labour in defiance of an official trade dispute.
