West Fraser Timber Co., North America's top lumber producer, is taking a hit from President Trump's latest round of tariffs on Canada. Its stock is one of the day's worst performers among forest and building-products shares.

The Vancouver, British Columbia, company that has sawmills and other wood-products facilities on both sides of the border is already contending with Trump's 10% national-security tariff on lumber as well as the long-standing duties on Canadian softwood exports. The 50% tariffs Trump announced last night exempt softwood lumber, which houses are framed with, but include plywood and specialty engineered wood products that West Fraser produces in western Canada.

Ultimately, West Fraser's exposure should be minimal because most of its products slated for the 50% levy are sold in Canada, according to TD Cowen analysts. They estimate that just 1% of West Fraser's aggregate sales would be exposed to the latest import taxes.

And that is assuming that the tariffs stick. For one, Trump is pursuing a novel application of Section 338 of the Trade Act of 1930 that could attract legal challenges. Also, the levies could be scrapped as part of the ongoing trade talks between the U.S., Canada and Mexico.

"Section 338 has a 30-day implementation period, which is an eternity in Trump's Washington," TD analyst Chris Krueger wrote in a note to the investment bank's clients. "That leaves ample time to hammer out some type of face-saving retaliation unwind."