Union leaders said the figure could be even higher.
A statement from Vimetco blamed a 50 percent drop in world aluminum prices for the planned layoffs at the Alro Slatina plant. Vimetco owns 84 percent of Alro Slatina.
The statement on Friday said that up to 1,200 people would be laid off and production halved. It added that a final decision regarding numbers would be made next week. Union leaders quoted by Hotnews news agency said that 1,800 of the 3,500 work force would be made redundant.
Some 400 workers on Friday protested the plans outside the factory in the southern town of Slatina. It is the biggest aluminum smelter in central and eastern Europe.
Alro Slatina's profits fell by more than 20 percent in the first nine months of 2009.