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 maintains 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 generate 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 each day since March 1.
This reduces output to 240 megawatts per generator, down from 360 or 392 megawatts, depending on the generator. The action is a protest against 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.
"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.
Despite demand peaking on hot days, the industrial action is unlikely to cause brownouts or blackouts due to an oversupply of electricity.
"The amount of available reserve is greater than the capacity of Yallourn," said an Australian Energy Market Operator spokeswoman.
EnergyAustralia was warned on February 25 the industrial action would last "for an indefinite period". 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 is expected to make a decision on Tuesday morning.
Commissioner Michelle Bissett of the Fair Work Commission declared on February 21 that the CFMEU's action was protected under the Fair Work Act. This was because the CFMEU had given EnergyAustralia enough notice and information about the action that it had an opportunity to avoid it.