General Motors Co. (GM) - Get Report  said Monday that it's laying off 415 workers at its Ramos Arizpe engine plant in Mexico as a three-week-old strike by the company's U.S. workers slows the company's operations down.

GM shut the Ramos plant's assembly lines that build V-8 engines and CVT transmissions, although production of four-cylinder engines continues at the site. The layoff represents 20% of the approximately 2,100-person workforce at the plant. The U.S. strike, launched Sept. 15 by 48,000 U.S. United Auto Workers members, has already pushed GM to lay off 6,000 workers at another GM factory in Silao, Mexico.

As the strike enters its fourth week, a UAW official said Sunday that negotiations "have taken a turn for the worse." The union expressed disappointment with GM's reaction to its latest proposal on wages, job security and other issues just one day after both sides had expressed hopes for a breakthrough.

Explaining the rejection of GM's latest contract offer, UAW Vice President Terry Dittes wrote in a letter to members Sunday that "we, in this 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."

But GM defended itself in a statement sent to TheStreet Sunday. The company said it continues to "negotiate in good faith with very good proposals that benefit employees today and build a stronger future for all of us."

This article is commentary by an independent contributor. At the time of publication, the author held TK positions in the stocks mentioned.