The steelworkers, at Sunshine Tube Mills, were told by the company on Monday that the plant would close by the end of January next year.
The job losses follow 50 other job cuts made in August, the union said.
The Australian Workers Union (AWU) said the company blamed price import competition for the closure.
It said although workers had raised productivity at the plant, the company was unable to compete against cheap Asian steel products being dumped in the Australian market.
AWU Victorian branch assistant secretary Cesar Melhem said the decision to close the plant was disappointing.
"We are extremely disappointed by the closure of the Sunshine Tube Mills because the workers have done everything possible to keep the operation viable, including cooperating in the cost-cutting program three months ago," Melhem said.
Workers would receive above-award redundancy payments and job search assistance, he said.
They will be paid their outstanding entitlements in full, including all long service leave, uncapped redundancy entitlements of four weeks pay for each year of service and a $5,000 closure payment.
Comment was being sought from the company.
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