Up to 80 workers will lose their jobs at Collie's Muja power station.
On Monday, the State Government announced two of the four operating units will be shut down from October 2022.
Premier Mark McGowan said to keep the units operating beyond that date would cost WA taxpayers an additional $350 million.
"It no longer makes sense to keep the Muja C units operational. They are expensive to run, and demand for electricity from the units is declining dramatically," he said.
"Keeping them open will lead to higher power bills for Western Australians and put our stable electricity supply at risk."
It is expected around 30 workers will be affected by the closure of the first Muja C Unit 5 on October 1, 2022.
A further 40-50 workers will be impacted by the Muja C Unit 6 closing on October 1, 2024.
The two Muja D units, Collie Power Station and Bluewaters will continue to operate.
"We will be working closely with Synergy to ensure all workers impacted by the closure will be supported and options are available, depending on their individual needs and future plans," Mr McGowan said.
18-year-old male from Lakelands charged over incident in Pinjarra
BREAKING: Reports of a man armed with a firearm in the Pinjarra area
Hayden Ballantyne signs with Rockingham Rams
Mayor reassures community that 'no decision has been made' to close 4WD access at Tim's Thicket, White Hills beaches
DBCA 'sick and tired' of illegal access to Port Kennedy Scientific Park
Mandurah homeless camp goes up in flames
Dawesville community shocked after kangaroo deliberately mowed down
Teens armed with knife, scooter charged over Rockingham Shopping Centre fight
Mandurah private school teacher charged with alleged sexual abuse of male student