US-Mexico trade includes significant business between auto suppliers and assembly plants that are interwoven in complex cross-border supply chains.
Products that are traded between the two countries tend to cross each other's borders multiple times.
Many automakers, including General Motors Co., ship vehicles manufactured in Mexico into the US Those cars could be subject to Trump's tariffs.
"The suddenly renewed potential for tariffs on goods from Mexico revives a risk (for automakers and suppliers) many believed was largely behind us" after the signing of the USMCA, said Itay Michaeli, auto analyst at Citi Research.
"This new uncertainty is a clear negative for auto stocks." Oxford Economics has forecast that 25 per cent US tariffs on Mexican imports, if maintained, could deal a heavy blow to the US economy. It estimated that the import taxes would subtract at least 0.7 percentage point from US economic growth in 2020, reducing growth to a frail 1 per cent or less.