The United Auto Workers union reached a tentative deal Thursday to raise wages 25% at Ultium Cells, a company that makes batteries for General Motors' electric vehicles.

The union said the agreement will be retroactive to December 23, meaning that workers will get between $3,000 to $7,000 in total back pay, depending upon the hours they worked.

About 1,100 hourly employees at the company's Warren, Ohio, factory are covered by the deal. Ultium, a joint venture between GM and Korean partner LG, is in the process of building two additional plants besides this one.

Industrywide, there are six US plants making EV batteries and 22 more under construction. The agreement announced Thursday is significant since the Ultium plant is the first US EV battery plant to be represented by a union.

The joint statement from the company and the union did not say what the workers are currently paid. Last month, the union disclosed that starting wages at the plant were $16.50 an hour, and they were set to rise to only $20 an hour after workers completed seven years on staff. Even with the raise, Ultium Cells' workers will still earn far less than UAW members at unionized auto plants currently making up to $32.32 an hour.

"This interim wage increase is only the first step as we progress towards a fair and comprehensive contract," said Josh Ayers, the chairman of the bargaining unit for UAW Local 1112, which represents the workers. "The UAW Local 1112 members working at Ultium Cells deserve this increase."

"We're proud to be able to reach an interim agreement for wage increases that prioritizes our incredible workforce," said Kareem Maine, Ultium's plant director at the Warren plant.

Union members at the plant are expected to decide whether or not to ratify the deal on Sunday.

The deal comes as the UAW is in the midst of negotiating new four-year contracts with GM, Ford and Stellantis, which produces vehicles under the Jeep, Ram, Dodge and Chrysler brands. All three companies are in the process of building battery plants with their own joint ventures as they shift from internal combustion vehicles to EVs.