The UAW's lead negotiator said Sunday that talks with General Motors have "taken a turn for the worse."

The surprise negative development followed reports of progress in recent days and adds more uncertainty to when the UAW's 3-week-old strike against GM might come to an end.

In fact, a person close to the talks told the Free Press that the bargaining had turned somewhat sour as GM walked back what had been a proposed solution for temporary workers.

Health care, as of Saturday, was resolved, meaning it would not change or cost members more. But the person said the union considers GM's last two proposals to be like ultimatums.

In a letter to union members around 11:30 a.m. Sunday, Terry Dittes, vice president for the UAW GM Department, said that the UAW on Saturday afternoon had prepared an extensive proposal and presented it to GM.

"Our proposal addressed issues of wages, signing bonus, job security, pensions, skilled trades, profit sharing, transfer rights; to name just a few," Dittes said.

GM responded at 9:05 a.m. Sunday, Dittes said.

"The company's response did not address our extensive package provided last evening," Dittes wrote. "They reverted back to their last rejected proposal and made little change. The company's response did nothing to advance a whole host of issues that are important to you and your families! It did nothing to provide job security during the term of this agreement."

He wrote that the union, "could not be more disappointed with General Motors who refuse to recognize the experience and talent of our membership who make their world class products and billions of dollars in profits."

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Dittes said that after making progress on key issues "a couple days ago, the company has shown an unwillingness to fairly compensate the great workforce of the UAW. These negotiations have taken a turn for the worse. Your issues are our issues, and our strength is with you, our great membership. We will continue to negotiate on behalf of you, your families and all workers in our country. "

GM provided a statement in response to Dittes' letter that defended the company's proposals:

“We continue to negotiate in good faith with very good proposals that benefit employees today and builds a stronger future for all of us. We are committed to continuing discussions around the clock to reach a resolution.”

Roughly 46,000 UAW workers went on strike against GM sites nationwide on Sept. 16 after the 2015 contract expired two days before. The union continued contracts with Ford and Fiat Chrysler Automobiles, following the customary plan to negotiate a deal with one company to use as a template for the other two.

A press release from the UAW Sunday afternoon included an email exchange between Dittes and Scott Sandefur, who is heading up negotiations for GM. The exchange highlighted the separation between the two sides as well as providing more details about the UAW proposal and response from GM.

"This package addressed a minimum of (35) hourly proposals and three (3) salaried proposals. Our extensive proposal package was an effort to move this set of negotiations to the next step to reach a tentative agreement," according to the Dittes email to Sandefur. "During your response to our proposal delivered at 9:05 a.m. today, Sunday, October 6, 2019, you didn't even have a professional courtesy to explain why you could not accept or why you rejected our package proposal for each item we addressed."

Dittes continued by saying, "we expect the company to respond and discuss the package proposal we presented yesterday. The law and basic decency require no less."

More:Striking UAW reports 'good progress' on health care and temp workers in GM talks

More:UAW regional director charged in corruption probe placed on leave as strike continues

The change in tone about the state of talks followed word on Saturday from a person familiar with negotiations that the remaining outstanding issues centered on pensions and 401(k)s and the narrowing of the pay gap for in-progression workers.

The negotiations have continued as more than 46,000 GM UAW workers have remained on strike. The spillover impact from the strike has led to plant shutdowns outside of the United States, supplier layoffs and substantially reduced pay for striking workers, who now get $250 per week from the union's strike fund.

Also this weekend, the Free Press reported that Vance Pearson, the director of the UAW region covering 17 states from Missouri to California, has been placed on leave. Pearson, who succeeded Gary Jones in the post when Jones became UAW president, is among those charged in an ongoing corruption probe. Jones has also faced scrutiny as his house was among those raided in August, and a source identified him as an unnamed union official who had $30,000 seized from his home.

Contact Jamie L. LaReau at 313-222-2149 or jlareau@freepress.com. Follow her on Twitter @jlareauan. Read more on General Motors and sign up for our autos newsletter.