Union members have been deliberately reducing electricity output at the Yallourn power station during the hottest parts of the afternoon as Victorians swelter through a record heatwave.
The industrial action reduces the electricity the plant's owner - EnergyAustralia - can sell into the market, although the nation's market regulator says power supplies have not been affected.
EnergyAustralia will on Tuesday seek court orders to end the action and wants compensation for the electricity it has not been able to sell. Hot days usually cause the highest demand for energy because more people use airconditioners.
Members of the Construction, Forestry, Mining and Energy Union have been using a manual override to reduce output at four generators between 4pm and 6pm every afternoon since March 1.
This reduces output to 240 megawatts for each generator, down from 360 megawatts or 392 megawatts, depending on the generator. CFMEU members are protesting over enterprise agreement negotiations.
EnergyAustralia spokesman, George Svigos, said the generator would seek to restore the output of Yallourn.
"We are taking the steps open to us to protect our business from losses," he said. "We remain willing to continue discussions in good faith. So it is particularly disappointing that the CFMEU has chosen to take action at this time. The effect of the CFMEU action is to prevent the Australian Energy Market Operator from being able to remotely determine the amount of electricity Yallourn should produce to meet demand.
"We are working through the issue of financial impact, but clearly reduced output at times of higher demand has had and will continue to have real cost implications for our business," he said.
However, despite electricity demand peaking on hot days, the industrial action was unlikely to cause brownouts or blackouts due to an oversupply of electricity.
"The amount of available reserve is greater than the capacity of Yallourn," a spokeswoman for the AEMO said. "[The action] would have no impact on our ability to meet demand. Even if Yallourn was completely off we would still be able to meet demand."
Yallourn supplies about 8 per cent of the needs of the National Electricity Market.
EnergyAustralia was warned on February 25 the industrial action would last indefinitely.
It has filed a writ seeking damages and orders restraining CFMEU members or their agents from reducing electricity output. The Supreme Court of Victoria heard the matter on Friday and was expected to make a decision on Tuesday morning.