Although there have been warnings of electricity blackouts within two years without immediate action to increase generating capacity, the Sunday Tribune has learned the state company is planning to close down 1,300 megawatts of generating capacity. It is taking this action to address concerns about its dominant position in the market and to help get clearance from the regulator to build a high-tech 400mw plant in Cork.

The closures are likely to be strongly resisted by the ESB unions. The company has already announced the planned closure of the Tarbert 600mw power plant, but it is understood that it wants to take a further 700mw out of the system with Poolbeg and North Wall in Dublin, Great Island in Waterford and Marina in Cork, all being looked at as potential targets.

These are all older plants operating in the so-called "mid merit" sector, where generators are powered for around two-thirds of the day.

It is in this sector that ESB is perceived as most dominant because the private sector is more interested in building "base load" stations that provide electricity 24 hours a day.

Members of the ATGWU in Tarbert have passed a motion stating that they will conduct a ballot for industrial action unless the company engages in discussions on the closure of Tarbert by next Wednesday.

Brendan Ogle of ATGWU accused ESB of "playing Russian roulette with energy supplies and our members' jobs and terms and conditions for an ideological experiment, re the opening up of the market which has no guarantee of success".

A spokesman for ESB declined to comment on the 1,300mw figure but confirmed there was an issue around the dominance of ESB's 'mid-merit' plant. "Our aspiration would be that the independent sector would take up the slack there is.

We'd expect to see other generators come in, " he said, adding that "whether it's attractive or not is a matter for the market".