GM also stopped operations at the transmission plant that supports Silao Assembly, along with a nearby engine plant that produces 6.0-liter V-8s for commercial vehicles built at U.S. factories. The closures in Silao resulted in about 6,000 temporary layoffs, a GM spokesman said.
GM was continuing to build the Chevrolet Blazer and GMC Terrain in Ramos Arizpe, Mexico, and the Chevy Equinox and Trax in San Luis Potosi, Mexico.
"Strikes hurt everyone," GM spokesman Jim Cain said. "The sooner it's resolved, the better."
GM last week said third-quarter sales jumped 29 percent for the GMC Sierra and 15 percent for the Chevy Silverado, which is trying to avoid finishing a year with less sales than both the Ford F series and Ram's pickups for the first time ever. The Silverado trailed Ram by almost 52,000 going into the fourth quarter.
"General Motors was on the right arc. This is going to hurt and hurt badly," said Steve Kalafer, CEO of Flemington Car and Truck Country in Flemington, N.J.
Combined, light-duty Sierras and Silverados made up nearly a quarter of GM's third-quarter U.S. deliveries.
"It's a tough time for them to be losing this," said Paul Waatti, an analyst at AutoPacific. "They're bleeding market share at the same time."
In the first nine months of the year, the Silverado held 22.6 percent of the full-size pickup market, down from 24.2 percent a year earlier, according to the Automotive News Data Center, and the Sierra had 9 percent, up from 8.7 percent at the same time in 2018. Ram's pickup share was 25.5 percent, up from 21.4 percent a year ago, and the Ford F series had 36.6 percent, down from 38.6 percent.
There was no production increase at Silao Assembly in anticipation of the strike, according to LMC Automotive. But GM spokesman Dan Flores told Automotive News that whenever the company faces a significant disruption, such as severe weather or a strike, "we do have teams that look at potential part shortages that would be a result of any issue."
GM will undoubtedly attempt to compensate for its lost production after the strike ends, but some will be tough to make up, said IHS Markit's principal auto analyst, Stephanie Brinley.
"The plants that were already running on overtime, the plants already running three shifts, it's hard to find a space to make up some of that volume," Brinley said. "This all depends on how long it goes, but it might end up impacting a little bit of sales early next year."