• Automaker shares dropped on Tuesday after President-elect Donald Trump threatened a 25% tariff on goods from Mexico and Canada.
• Companies like General Motors and Stellantis have major manufacturing presences in Mexico and Canada.
• Trump had been expected to renegotiate the regional trade deal he reached during his first term.

DETROIT – Shares of automakers General Motors and Stellantis fell Tuesday morning after President-elect Donald Trump threatened to put 25% tariffs on goods imported from Canada and Mexico into the U.S.

Such tariffs would have a major impact on the global automotive industry, which has used the countries, particularly Mexico, for lower-cost production of vehicles since the North American Free Trade Agreement went into effect in 1994.

UBS reports the automotive industry is responsible for 26% of imports from Mexico to the U.S., including vehicles and parts, and 12% from Canada.

Nearly every major automaker operating in the U.S. has factories in Mexico, however GM and Stellantis produce highly profitable full-size pickup trucks there.

Shares of GM, which has five large assembly plants in the countries that Barclays estimates will produce 1 million vehicles this year, were down more than 8% during midday trading Tuesday.

Chrysler parent Stellantis, which has four major plants in the countries, dropped more than 5%. Shares of Ford Motor, which has less exposure in the countries, were down 2%. Shares of Toyota Motor, Honda Motor and others with production in Mexico also were down at least 1%.

Trump announced he intends to levy a 25% tariff on all U.S. imports from Canada and Mexico using an executive order when he is inaugurated on Jan. 20. He also announced plans to raise tariffs by an additional 10% on all Chinese goods coming into the U.S.

Such tariffs would be more aggressive than what was expected to be Trump's plan, a renegotiation of the United States-Mexico-Canada Agreement, which he hashed out during his first term to replace the North American Free Trade Agreement. Such a move would end the regional free trade deal.

Spokespeople for GM and Stellantis declined to comment Tuesday on the potential tariffs. The American Automotive Policy Council, a lobbying group for the two automakers and Ford, did not immediately respond for comment.

Wall Street analysts viewed Trump's announced tariff plans as a shot across the bow at the countries to create leverage in any upcoming negotiations.

"Our view is that the threat of tariffs is the instrument Trump would use to extract from other countries the economic and political outcomes that he considers best for America," BofA Securities' Carlos Capistran said in a Tuesday note. "We expect Canada and Mexico to show willingness to negotiate on the above issues to avoid tariffs."

Barclays' Dan Levy agreed in an investor note Monday night: "We view [the] announcement as largely negotiation tactics (as seen in 2016), and see such magnitude of tariffs unlikely."

Trump and Democrats alike said they believe the trade deal needs to be changed to address potential plans for Chinese manufacturers such as BYD.

Trump floated several tariff proposals during his campaign, including calling for a more than 200% duty or tax to be levied on imported vehicles from Mexico. He also has threatened, as he did during his first term in office, to increase tariffs on European vehicles.

– CNBC's Michael Bloom contributed to this report.