If you thought the summer trade battles were intense, September has rewritten the rulebook. In just a matter of weeks, the trade relationship between the United States and Canada has devolved into a historic tit-for-tat escalation, deploying legal mechanisms that haven’t been seen since the Great Depression.
At the center of this battle is the Trump administration’s aggressive use of Section 338 of the Tariff Act of 1930—a lever designed to punish foreign countries that discriminate against U.S. commerce.
Here is exactly what went down this month, and which industries are caught in the crossfire.
The Escalation Timeline
The U.S. implements sweeping 50% tariffs on roughly $27.6 billion worth of Canadian imports under Section 338.
Canada strikes back. The Canadian government officially launches “dollar-for-dollar” retaliatory tariffs of 15%, 25%, and 50% on U.S. goods covering the exact same $27.6 billion value.
On the exact same day Canada’s retaliation takes effect, President Trump signs a series of new proclamations. The most severe action completely bans the importation of certain Canadian dairy products, alcoholic beverages, and motorcycles, set to take effect on September 29.
A second wave of U.S. proclamations goes into effect. Section 338 tariffs are expanded to cover Canadian paper products, cheeses, and motorboats. Furthermore, the administration announces that these Section 338 tariffs will now “stack” on top of existing Section 232 national security tariffs, pushing total duty rates up to 100% on items like steel and aluminum.
Who is Paying the Price?
Canada’s September 8 countermeasures were highly targeted. According to the official List of products from the United States subject to counter-tariffs, Ottawa is squeezing specific sectors to maximize political pressure in the U.S.
The hardest hit American exports into Canada currently include:
- Dairy & Agriculture: Milk powders, whey, and appliances.
- Heavy Industry: Agricultural equipment, appliances, and certain electronics.
- Raw Materials: Steel, aluminum, and pulp/paper products.
Meanwhile, the U.S. is utilizing the ultimate weapon in the trade arsenal: total exclusion. By banning the entry of specific Canadian goods like non-alcoholic beer, molasses, and motorcycles, the U.S. is signaling that it is willing to entirely sever specific supply chains rather than just tax them.
What Does “Tariff Stacking” Mean for Importers?
Perhaps the most alarming development for cross-border businesses is the new reality of tariff stacking.
Previously, certain goods were exempt from the Section 338 actions if they were already being hit by Section 232 (national security) tariffs. As of September 15, that exemption is gone. If you are importing Canadian steel or automotive components, you may now have to pay the Section 232 rate plus the 50% Section 338 rate. For some supply chains, this effectively doubles the cost of raw materials overnight, rendering Canadian sourcing financially impossible.
Source: Legal analysis detailing the unprecedented use of Section 338 and the non-renewal stakes for the USMCA by Benesch Law