The United Auto Workers has filed a petition for election on behalf of workers at an Ultium Cells plant in Ohio, claiming the company is refusing to recognize cards that the employees signed to join the union.

Ultium is a joint venture between General Motors and LG Energy Solution.

The petition was filed with the Cleveland office of the National Labor Relations Board for 900 workers at the Ultium plant in Warren, Ohio.

The International Union, United Automobile, Aerospace and Agricultural Implement Workers of America said that Ultium previously engaged in talks with them about a process for certifying the union’s majority status without going through an National Labor Relations Board election.

“Make no mistake: whether it is by card check or union election, these workers will be members of the UAW,” Ray Curry, UAW President, said in a prepared statement Monday.

Ultium said it respects workers’ right to choose union representation and will comply with the National Labor Relations Act, which protects employees’ right to freely decide unionization through a voluntary election conducted by the NLRB.

“Ultium Cells believes the right to a personal and private vote is important,” the company said.