Alcoa Corp. AA, said Wednesday that it plans to begin on June 25 a formal process at its San Ciprian aluminum facility in Spain that could lead to up to 534 jobs being cut. 

The company said it had started in May talks with the workers' representatives regarding the "significant and unsustainable circumstances" at the plant. Alcoa said the aluminum smelter has suffered "significant and recurring financial losses," which the company expects to continue. 

The alumina refinery at San Ciprian is not affected by the restructuring. 

The stock, which was indicated up fractionally in premarket trading, has rallied 65.0% over the past three months, while the S&P 500 SPX, -0.36% has climbed 23.6%.