(Reuters) -The United Auto Workers union said on Monday some local units representing workers at Stellantis are preparing to file grievances and could launch a nationwide strike, accusing the automaker of not honoring production commitments.

The UAW said the locals represent tens of thousands of workers and the dispute is over agreements the union said Stellantis made in 2023 as part of a new labor agreement.

Chrysler-parent Stellantis agreed to build a new $3.2 billion battery plant and invest $1.5 billion in a new mid-size truck factory in Belvidere, Illinois and add 5,000 total U.S. jobs by 2028 as part of a new contract deal, the UAW said in November 2023.

Stellantis did not immediately respond to requests for comment. The UAW said the automaker would not launch the Illinois investments on the previously agreed timetable, without specifying the dates.

Last month, the U.S. Energy Department said it planned to award Stellantis $334.8 million to convert the shuttered Belvidere Assembly plant to build EVs and $250 million to convert its Indiana Transmission Plant in Kokomo to produce EV components.

The UAW said since 2023 "the company has gone back on its product commitments at Belvidere, and has been unreceptive in talks with the union to stay on track." The UAW added "this glaring violation of the contract imperils all of the other investment commitments the company has made."

UAW President Shawn Fain referred to the issue during a prime-time address at the Democratic National Convention on Monday night."Let me be clear: Stellantis must keep the promises they made to America and our union contract. And the UAW will take whatever action necessary at Stellantis or any other corporation to stand up and hold corporate America accountable," he said.

Earlier this month, Stellantis said it was laying off as many as 2,450 factory workers from its Warren Truck assembly plant outside of Detroit as the automaker ends production of the Ram 1500 Classic truck.

Stellantis said last month it was offering a new round of voluntary buyouts to its U.S. salaried workers, the latest in a series of cost-cutting measures CEO Carlos Tavares is implementing at the company's American operations.