A strike by the UAW has closed the only U.S. plants operated by a major supplier of the low-voltage batteries used by automakers and the aftermarket, according to WardsAuto. More than 500 members of Local 12 in Toledo, Ohio left their jobs May 8 at the Clarios battery plant in nearby Holland, Ohio, after they overwhelmingly rejected the company’s last proposal. The plants makes 12V and 48V batteries. The vote to turn down the contract was nearly unanimous, according to union reps.

The plants manufactures about 150,000 batteries a week for customers including Ford and General Motors. “Our Toledo facility opened in 1981 and today employs around 650 represented and salaried employees. Toledo is a key location for Clarios and has been a focus of recent investment as we anticipate our ability to competitively support growth and increased customer demand well into the future,” Clarios said in a statement. “Negotiations have been ongoing since April. The contract expired April 19. Unfortunately, on April 27, our represented employees did not ratify the proposed agreement despite having the support of their bargaining committee,” the company said.

“We’ve been working in good faith to come up with an agreement. We remain optimistic as we’ve reached agreements with all of our unions during recent contract negotiations. Unfortunately, our first offer was not accepted, but we are dedicated to continuing good-faith negotiations to reach a contract that focuses on the future and supports our customers,” Clarios said.

Clarios spokesman Zach Peterson said he couldn’t comment on shipments to customers, which cover a broad range of vehicle manufacturers from makers of heavy trucks to light vehicles as well as aftermarket outlets such as AutoZone. On its website, Clarios, which also operates plants in Mexico, Europe and China, notes one of every three vehicles around the world uses one of its batteries, which are sold under a variety of brand names.

The strike at the Clarios plant could serve as an early test for Shawn Fain, the UAW’s new president, who has promised the union would rejoin “the fight” for better wages and working conditions. Fain has said the UAW would not automatically fall in line with an endorsement of President Joe Biden in his 2024 re-election bid. Fain says Democrat Biden, who has enjoyed union support throughout his long political career, must provide more support for union members and the UAW in the transition to electric vehicles. “Your elected leadership on the International Executive Board are united and hard at work implementing the changes we believe are needed to transform our union back into a fighting organization. But it’s going to take all of us to get back in the fight,” Fain said.