By Victor Reklaitis

Detroit's Big Three deal with new threat on Monday - and that's after missing out on a possible tariff reprieve over the weekend

A Ford Motor plant in Windsor, Canada, is shown in this photo from last year.

U.S. President Donald Trump escalated his trade fight with Canada on Monday, threatening a new 50% tariff on Canadian-built automobiles starting Jan. 1 after imposing a separate set of 50% tariffs on his northern neighbor over the weekend.

Shares in the Big Three U.S. automakers, all of which have production facilities in Canada, were losing ground during Monday's session. General Motors (GM) fell 2.2%, Ford (F) shed 4%, and Jeep parent Stellantis (STLA) dropped 4.3%, while the broad S&P 500 index SPX slipped 0.2%.

"On January First, 2027, Tariffs on all Cars, Trucks, both large and small, Automotive Parts, and Steel, will be increased to 50%," Trump said in a social-media post. "Build in the U.S. and there are ZERO TARIFFS."

Even before Monday's decline, the Big Three automakers already had been dealt a setback early Saturday when a new trade deal between the U.S. and Canada failed to get finalized, leading the Trump administration to roll out its 50% tariffs on $20 billion worth of Canadian imports - and spurring Canada to announce retaliatory levies that will start Sept. 8.

If the deal had gone into effect, U.S. tariffs on Canadian-built automobiles had been expected to drop to 15% from 25% - in what would have been a win for Detroit's Big Three. Instead, their Canadian factories face an increase in the U.S. tariffs on their products in about four months. Meanwhile, automobiles built in the European Union, Japan and South Korea enjoy a U.S. tariff rate of 15%.

The trade group that represents Ford, GM and Stellantis has previously complained about trade policies that provide lower tariffs for vehicles imported from Asia or Europe than for North American-built vehicles with high U.S. content.

American home builders also are viewed as among the big losers due to the new trade tensions between the U.S. and Canada.

The Canadian goods facing new 50% U.S. tariffs as of early Saturday include construction materials such as cement, paints, plywood, medium-density fiberboard and particle board.

The new U.S. tariff plan for Canada was first floated in late July, and the National Association of Home Builders offered a warning at that time. "With housing affordability already near historic lows, we continue to urge the Trump administration to exempt building materials from its broader tariff strategy and avoid new trade barriers that could worsen the housing crisis," the NAHB said last month.

While certain U.S. sectors are facing headwinds from the new tariffs on Canadian goods, analysts have said the broad economic effects of the levies could be modest for the U.S. overall, as they only cover about 5% of total Canadian imports.

-Victor Reklaitis

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08-24-26 1146ET