DETROIT (AP) — The United Auto Workers union says it has filed unfair labor practice complaints against Stellantis and General Motors for failing to make counteroffers to the union's economic demands.

Ford was the only company of the Detroit Three to make a counteroffer, but it rejected most of the union's proposals, President Shawn Fain told workers Thursday in a Facebook Live meeting.

Fain's statements and strong responses from the companies showed both sides appear to be digging in with just two weeks before contracts with the union's 146,000 members expire. Fain is once again threatening to strike when the pacts end at 11:59 p.m. Sept. 14.

He told members that the companies have been warned not to wait until the last minute to get serious about bargaining.

"The Big Three are either not listening or they are not taking us seriously," Fain said, calling the refusal to respond "insulting and counterproductive," and also illegal. He said the union filed the complaints with the National Labor Relations Board on Thursday.

In a statement, Stellantis said the unfair labor charges are not based on fact, and that it will vigorously defend itself against them.

"We are disappointed to learn that Mr. Fain is more focused on filing frivolous legal charges than on actual bargaining," the statement said. "We will not allow Mr. Fain's tactics to distract us from that important work to secure the future for our employees."

Ford said it made a fair economic proposal that is better than the pay at Tesla or foreign automakers.

"We will not make a deal that endangers our ability to invest, grow and share profits with our employees," CEO Jim Farley said in a statement. "That would mortgage our future and would be harmful to everyone with a stake in Ford."

GM said it strongly refutes the union's labor accusation.

"We believe it has no merit and is an insult to the bargaining committees," GM said in a statement. "We have been hyper-focused on negotiating directly and in good faith with the UAW and are making progress."

Automakers have said they're facing an uncertain transition from gas-powered vehicles to those that run on batteries. They're also reluctant to take on labor costs that grow even farther beyond those at Tesla and foreign automakers with U.S. factories.

Fain, who won the UAW's presidency this spring in its first direct election of officers by members, has set expectations high, telling workers that they can make significant gains if they're willing to walk picket lines.

But even he has described union demands as audacious. Union members are seeking 46% pay raises over four years, restoration of traditional defined-benefit pensions for new hires, an end to tiers of wages, pension increases for retirees, and a 32-hour work week for 40 hours of pay.

Top-scale assembly plant workers now make $32 per hour, but the union's proposal would raise that to $47.

Ford offered a 9% general wage increase over the life of the four-year contract, with lump sum payments instead of the union's proposed cost-of-living adjustments, Fain said. The company also rejected demands to end tiers of wages, instead proposing that it take six years for new hires to reach the top of the pay scale rather than the current eight, he said.

Ford also turned down union demands to increase pension payments to retirees and for companies to pay workers if their plants are closed, Fain said. And it still plans to move battery work to what Fain called low-paying jobs outside of Ford at joint venture battery plants.

"Our union isn't going to stand by while they replace oil barons with battery barons," Fain said.

Ford said offered to end wage tiers and said its proposal would give workers 15% guaranteed wage increases and lump sums, and improved benefits during the four-year contract. It said wages, including overtime and lump sum bonuses, would rise from an average of $78,000 per year last year to $92,000 in the first year of a new contract.

Workers would get $5,500 in ratification bonuses and $12,000 in cost-of-living payments during the contract, Ford said.

In addition, workers would get health care coverage worth $17,500 and other benefits worth another $20,500, the company said.

Fain has said the union could strike all three automakers at once, or it could pick a target company. Earlier this week, Canadian auto workers, whose contracts expire four days after the UAW's, selected Ford as their target.