Alcoa posted its worst day since 2009 after the U.S. Treasury Department issued a six-month reprieve on sanctions levied against a top Russian aluminum competitor.
Its stock fell more than 13.5 percent after the department said it would give Americans until October to wind down transactions with Rusal, the stock's worst performance in a single day since March 30, 2009. The extension was granted, Treasury Secretary Steven Mnuchin said, to give the department time to review its penalties on the company.
Aluminum prices also fell.
"Rusal has felt the impact of U.S. sanctions because of its entanglement with Oleg Deripaska, but the U.S. government is not targeting the hardworking people who depend on Rusal and its subsidiaries," Mnuchin said in a statement Monday.
"Rusal has approached us to petition for delisting. Given the impact on our partners and allies, we are issuing a general license extending the maintenance and wind-down period while we consider Rusal's petition," Mnuchin added.
The latest decision from the Treasury Department sent aluminum prices swinging more than 5 percent lower.
Moscow's Rusal was targeted during a wave of harsh U.S. sanctions earlier in April, freezing all of the company's assets within U.S. jurisdiction.
Deripaska, a billionaire oligarch who previously ran Rusal, was also slapped with sanctions and has been charged in special counsel Robert Mueller's investigation regarding Russian involvement in the 2016 U.S. presidential election.
Alcoa did not wish to comment for this story at the time of its publication.