WARREN, OH—Workers will vote this week whether to unionize at Ultium Cells’ battery assembly plant here.

The National Labor Relations Board (NLRB) said workers at the factory, a joint venture between General Motors and LG Energy, will vote Dec. 7-8 after the United Auto Workers (UAW) petitioned to represent about 900 workers there.

The vote is a crucial test of the UAW’s ability to organize workers in the growing electric vehicle supply chain. The UAW petition sought the election after a majority of employees signed cards authorizing the union to represent them.

An Ultium spokesperson said the venture “respects workers’ right to choose union representation and the efforts of the UAW to organize battery cell manufacturing workers at our Ohio manufacturing site.”

The plant, which began production in August, is the first of at least four planned Ultium battery factories in the U.S.