Workers at a Clarios vehicle battery plant in Holland, Ohio, began striking Monday morning after voting down a contract proposal, local TV news station 13abc reported. The approximately 400 striking workers are members of UAW Local 12.

Clarios is a leading global producer of low-voltage batteries for a range of vehicles, with 18 plants and more than 5,800 employees in the U.S. The Holland plant, near Toledo, employs about 650 employees and produces 125,000 to 150,000 batteries a week for Ford and General Motors.

“This is really going to hurt their delivery to these companies,” Bruce Baumhower, president of UAW Local 12, told Automotive News.

“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,” a company spokesperson said.

Contract negotiations at the plant began in April, with a previous contract expiring April 19. On April 27, UAW-represented employees voted against ratifying a proposed agreement that, according to Clarios, had the support of the bargaining committee. But 13abc reported the proposal was voted down by 98 percent.

Clarios and the union have not been able to reach an agreement on several issues, including overtime pay, Baumhower said. Under the old contract, workers received time-and-a-half pay for anything over eight hours a day, but on the company’s recent proposal, straight pay was extended to 12 hours a day.

Workers at the plant do not want to be on strike, Baumhower said, but the pay cuts resulting from the changes to overtime pay are too significant to absorb.

This is the first strike at the plant, which was operated by Johnson Controls until 2019, since it opened in 1982. Baumhower said negotiations have become more difficult in recent years.

“We’ve implemented a contingency plan that allows for limited operations at our facility and will continue to evaluate how to best support our customers,” the Clarios spokesperson said.

Clarios, of Milwaukee, ranks No. 75 on Automotive News’ list of the top 100 global parts suppliers, with estimated parts sales to automakers worldwide of $2.5 billion in its fiscal 2021.