DETROIT — General Motors' first wage-and-benefit offer to the United Auto Workers on Thursday fell far short of the union's initial demands.

The offer comes just a week before the UAW's national contracts with GM, Stellantis and Ford expire, and even though both sides are far apart, it's a sign of movement on economic issues.

Still, union President Shawn Fain called the offer “insulting." He is threatening to strike against any automaker that hasn't reached a tentative agreement by the time contracts expire at 11:59 p.m. on Sept. 14. A strike against one or more automakers by up to 146,000 autoworkers is a real possibility.

GM said in a letter to workers that it's offering a 10% wage increase during a new four-year contract, plus two more 3% one-time payments. It's also offering a $6,000 inflation payment, $5,000 more in lump sums to protect against inflation during the contract, and a $5,000 contract ratification bonus. The company wouldn't say when the pay raises or most of the lump sums would be effective.

The wage offer is slightly better than one from Ford that was rejected by the union last week. Its reliance on lump-sum payments rather than annual pay raises is contrary to what Fain has been seeking.

The union also said GM rejected its demand to increase retiree pension payments and kept lower tiers of pay at component plants and parts warehouses.

Last week the UAW filed unfair labor practices complaints against GM and Stellantis with the National Labor Relations Board. At the time, though, neither company had made a counterproposal to the union's economic demands.

The union, citing large company profits over the last decade and CEO pay raises, is seeking 46% across-the-board pay raises over four years, a 32-hour week with 40 hours of pay, restoration of traditional pensions for new hires, union representation of workers at new battery plants, restoration of traditional pensions and elimination of wage tiers. Top-scale UAW assembly plant workers make about $32 an hour, plus annual profit-sharing checks.

In a text message through a spokesman Thursday, Fain said the proposal “doesn’t come close to an equitable agreement.”

He accused GM of failing to bargain in good faith for the past six weeks, and making the offer only after the union filed complaints with the NLRB.

“GM either doesn’t care or isn’t listening when we say we need economic justice at GM,” Fain wrote. “The clock is ticking. Stop wasting our members’ time.”

In GM’s letter to employees signed by President Mark Reuss and manufacturing chief Gerald Johnson, the company said the wage increases it proposed are the largest since the 1999 contract.

“Our offer includes well-deserved wage improvements that far exceed the 2019 agreement and reward you for your hard work,” the letter said. “We still have work to do, but we wanted to make this offer to show our good faith efforts to keep the process moving.”

The union was scheduled to make another offer in response to Ford's on Thursday. Stellantis said it would have a counterproposal by the end of the week.

In an interview with The Associated Press on Wednesday, Fain conceded that the union won't get all of its demands in bargaining. He said the UAW would go on strike next week against any of the three automakers that have not reached a tentative contract agreement.