Ultium Cells' factory in the U.S. state of Ohio is seen in this July 2023 file photo. AP-Yonhap

Korean battery makers running joint factories with U.S. carmakers are facing surging labor costs as they have no choice but to sharply raise wages for their American employees amid growing union influence, according to industry officials, Tuesday.

Ultium Cells, the joint venture between LG Energy Solution and General Motors (GM), reached a tentative agreement with the United Auto Workers (UAW) on Monday (local time) for a 30 percent wage hike over three years. This came after Ultium Cells and the UAW agreed last August to increase the factory workers' wage by 25 percent on average.

"Eighteen months ago, this company was on a low road path to poverty wages, unsafe conditions and a dark future for battery workers in America," UAW President Shawn Fain said. "Now they've more than doubled their wages by the end of this contract, won record health and safety language and showed the world what it means to win a just transition."

UAW Local 1112 Shop Chairman Josh Ayers also said that the union wants this agreement to become a cornerstone for current and future battery plants across the nation.

Their remarks indicate that the UAW will flex its muscle once again against other joint battery plants that Samsung SDI and SK On run with U.S. carmakers.

U.S. President Joe Biden speaks as he joins striking United Auto Workers on the picket line in Michigan in this September 2023 file photo. AP-Yonhap

Based on strong support from U.S. President Joe Biden, the union has urged the joint ventures to raise wages and guarantee job security. After the UAW's strike last year, GM, Ford Motor and Stellantis agreed to a 25 percent wage increase over four years.

"The recent deal between Ultium Cells and the UAW is expected to affect other battery firms and carmakers in the U.S.," Korea Investors Service analyst Kim Ho-seop said. "Rising labor costs will be a negative factor for their business amid the slow demand for electric vehicles."

Last year, the UAW criticized StarPlus Energy, as the joint venture between Samsung SDI and Stellantis had not informed union leaders in advance of the construction of its Kokomo factory until a day before the announcement. Amid the growing pressure from the union, Samsung SDI is also preparing to open a joint battery plant with GM.

BlueOval SK raised salaries for its workers during the UAW's strike last year, although the joint venture between SK On and Ford said the wage increase was not related to the strike.

However, Ford said at that time that it remains open to the possibility of working with the UAW on future battery plants in the U.S.

"Three of the four battery plants under construction are part of the BlueOval SK joint venture between Ford and SK On," the U.S. carmaker said. "The future employees at these operations can choose to be union represented and enter into the collective bargaining process."