One of the largest unions in the ESB, the ATGWU, has withdrawn from the ESB Group of Unions.
The ATGWU said tensions had been apparent within the group of unions for some time.
Regional Industrial Organiser Brendan Ogle said neither his union nor its officers would attend any further meetings of the ESB Group of Unions as currently constituted.
However, he said they would accept an invitation from Congress General Secretary David Begg to a meeting this Friday to discuss the escalating rift among the unions.
The ATGWU decision follows a major row within the group of unions, in the course of which one union, the Technical, Engineering & Electrical Union (TEEU), had sought a meeting to force the removal of three senior officials of the group.
However, the TEEU backed down after Group Secretary Paddy Reilly threatened to seek a High Court injunction to stop that meeting going ahead.
The TEEU is also considering its position within the group of unions.
Mr Reilly said he could not comment on the ATGWU's departure from the group of unions at this point in time.
Dispute over La Cumbre position continues
In a separate development, representatives of ESB power station staff were meeting today to consider industrial action in the continuing dispute over the position of the company's deputy chairman and worker director, Joe La Cumbre.
Last week around 1,000 network technicians belonging to the TEEU voted to take 'whatever action was necessary' unless Mr Lacumbre is reinstated to his position by the next ESB board meeting on 22 February.
He says he was effectively removed from his position two weeks ago after a row with company chairman Tadhg O'Donoghue over the company's €0.5 billion pensions deficit.
