President Donald Trump’s threat of 50% auto tariffs on all imports from Canada is just the latest action to rattle an industry that’s endured shifting trade rules since he returned to office.

Trump issued the auto tariff plans early Monday, just as trade tensions between the two neighbors ratcheted up. On Saturday, the US slapped 50% tariffs on a much more limited group of Canadian exports after efforts to strike a deal collapsed.

But the steep auto tariffs, if enacted, could disrupt long-established business practices and have far-reaching consequences across the auto industry, experts say.

“Sweaters, honey and hockey sticks are not a trade war. What the president just threatened this morning is a trade war,” said Patrick Anderson, CEO of Anderson Economic Group, a Michigan-based consulting firm. “It would be a body blow to the auto industry. We would see plants closing on both sides of the border.”

Canada does have a large trade surplus with the United States. But when it comes to the auto industry, it’s the opposite — the US has a nearly $1 billion a month trade surplus with Canada.