Official figures showed that about one-third of last night's peak power use was supplied from interstate.

After a hearing in the NSW Industrial Relations Commission in Newcastle late yesterday, Unions NSW spokesman Peter McPherson said that Delta Electricity's Vales Point and Munmorah power stations were shut, while Wallerawang, near Lithgow, had one of its two units broken down.

Delta Electricity declined to comment on the situation but did not dispute the union's account of the generator outages.

At the hearing before commission deputy president Rod Harrison, Macquarie Generation representative Ken Petersen said the unions had threatened "the closure" of Liddell power station, near Singleton, a claim disputed by Mr McPherson and other union officials at the hearing.

They did not contest Mr Petersen's statements that conveyors clogged with wet coal meant that Liddell was fast running out of fuel, and had been forced to "shed load" to run at lower output on the three generators it had in service.

While the third state-owned generator, Eraring Energy, had not been affected by breakdowns, it joined MacGen and Delta in condemning the industrial action undertaken by unions in an effort to have the State Government's power privatisation plans overturned.

Mr McPherson said Delta had "been unlucky" in having its generators fail during the overtime bans but he said the unions had authorised workers to break the bans, if necessary, to maintain security of power supply and public safety.

Information from the National Electricity Market Management Company (NEMMCO), showed last night that NSW power use had peaked at about 11,700 megawatts about 6pm, when NSW had about 8200 megawatts of generating capacity.

The wholesale price had risen accordingly, to about $170 a megawatt-hour or four times this year's average price.