The UAW petition filed on Monday with the National Labor Relations Board (NLRB) and seen by Reuters seeks a Dec. 7-8 election of workers at Ultium Cells after a majority of employees had signed cards authorizing the union to represent them.

An Ultium spokeswoman on Wednesday did not say if it supports the election date proposed by the UAW but said, "We will be following the process outlined by the NLRB."

In August, the Warren, Ohio Ultium plant began production, the first of least four planned U.S. battery factories by the joint venture.

"By refusing to recognize their majority will, Ultium - which is a joint venture between General Motors and LG Energy Solution - has decided to ignore democracy and delay the recognition process," UAW President Ray Curry said in a statement.

U.S. President Joe Biden in a trip to South Korea in May expressed support for workers seeking to unionize joint-venture battery plants. Detroit's Big Three automakers all have battery plants in the works with Korean partners.

South Korea and the Biden administration have sparred over a U.S. decision in August to revise a tax credit making all EVs assembled outside North America immediately ineligible for tax credits, including all current Hyundai GM.N and Kia EVs for sale in the United States.

GM and LG Energy are considering an Indiana site for a fourth U.S. battery plant. They are already building a $2.6 billion battery cell plant in Michigan, set to open in 2024, and a $2.3 billion Tennessee plant to be completed in 2023.

(Reporting by David Shepardson; Editing by Mark Portedr)

By David Shepardson