Australia’s consumer watchdog says it will oppose AGL Energy’s planned takeover of two NSW government-owned power stations.

The Australian Competition and Consumer Commission (ACCC) says the proposed purchase of Macquarie Generation, which owns the Bayswater and Liddell power stations, would substantially lessen competition in the electricity market.

Macquarie Generation accounts for just over a quarter of NSW’s energy production.

ACCC chairman Rod Sims said the acquisition would mean up to 80 per cent of the state’s energy generation would be controlled by three companies: AGL, Origin and EnergyAustralia.

“This is likely to raise barriers to entry and expansion for other electricity retailers in NSW and, therefore, reduce competition compared to the situation if the proposed acquisition does not proceed,” he said in a statement on Tuesday.

Mr Sims said the three companies already had more than 85 per cent of the energy retail market and 95 per cent of the mass market between them.

NSW Treasurer Mike Baird said the ACCC decision meant the transaction would not proceed in its current form and the government would now consider the details of the ACCC review before deciding upon its next step.

He said the government was “not involved in a desperate fire sale” and would not consider a sale unless it exceeded the state’s retention value.

“I have always made it very clear we will proceed with the sale of state-owned assets only if it is in the best interests of taxpayers,” Mr Baird said in a statement.

He said the sale processes for remaining state-owned energy assets – Green State Power and Delta Electricity’s Central Coast power stations Vales Point and Colongra – were ongoing with both expected to conclude in 2014.

In a statement, AGL said it was reviewing the reasons for the ACCC’s decision and would decide what action to take in due course.