General Motors Co.'s assembly plant in Silao, a city in Mexico's automotive heartland, cranked out more than 400,000 highly profitable, large pickup trucks last year and is critical to the launch of a new generation of Chevrolet Silverado trucks later this year.

Now, GM's Silao factory, and the profit it generates, are at risk.

If U.S. President Donald Trump follows up on threats to dump the North American Free Trade Agreement, pickup trucks built at Silao and shipped to the United States could be hit with a 25 percent tariff, known in the auto industry as the "chicken tax."