More than 400 jobs will be lost when Alcoa closes its western Sydney plant.
The AWU says the company's announcement on Tuesday that it will close the Yennora plant is devastating news for a region already reeling from job losses.
The aluminium giant says it will close its Point Henry aluminium smelter at Geelong in August, its rolling mill in Geelong and a second rolling mill in Yennora, NSW.
The decision will affect more than 1000 workers across the three sites.
AWU NSW Secretary Russ Collison says the global oversupply of aluminium has played havoc with Australian operations.
"Our members at Yennora have lived with uncertainty for far too long. As the dollar has soared, the price of aluminium has plummeted," he said in statement.
"Both federal and state governments need to urgently put their shoulder to the wheel and develop a jobs plan for manufacturing in western Sydney.
"Let's be very clear - this closure is not about wages and conditions. The AWU has always made job security its number one priority."
An Alcoa statement said a strategic review found the 50-year-old Point Henry smelter had no prospect of becoming financially viable.
Meanwhile, the two rolling mills had been impacted by excess capacity in the Australian and Asian markets.
"Despite the hard work of the local teams, these assets are no longer competitive and are not financially sustainable today or into the future," Alcoa chief executive Klaus Kleinfeld said.
