Wind power company Airtricity is to pull out of the electricity market for residential users, leaving ESB as the only provider.
Airtricity has written to its 8,000 domestic customers and 3,000 of its larger commercial users to tell them they should change suppliers or face a huge increases in bills.
The company says it is facing big increases in the prices it is paying for power, and has criticised the energy regulator.
The Commission for Energy Regulation, CER, says it rejects Airtricity's contention that there has been market or regulatory failure and that the Commission is ignoring the ministerial direction of July 1999 on the trading arrangement for electricity.
It says it has been carrying out its own investigation of why electricity market prices were higher from last August and will be publishing its report by the end of the week.
It says it is especially looking at the impact of international fuel price increases and the effect which the availability of all generating stations on the system may have had on prices.
