Trump dusts off a 1930 law to hit Canada

The administration imposed an immediate 50 per cent tariff on imports from Canada on 19 August, using Section 338 of the Tariff Act of 1930. The century-old provision, written to punish foreign trade discrimination, had lain unused for decades.

An old weapon, dusted off

Section 338 gives the president broad and loosely limited power to impose retaliatory tariffs of up to 50 per cent on countries that "discriminate against the commerce of the United States". By going around modern trade agreements and relying on a Smoot-Hawley-era clause that has never been tested in court, the administration aimed to punish Canada's dairy supply-management rules and its provincial digital taxes while avoiding the limits of the Trade Act of 1974.

The choice of statute says as much as the rate. Tariffs imposed under emergency powers in 2025 were ruled unlawful by the Court of International Trade and then by an appeals court, which gave the administration reason to look for laws with more specific wording. Canada had already given ground once, scrapping its federal digital services tax in June 2025 under American pressure, and the target has now shifted to provincial levies and to the dairy quota system that successive Canadian governments have defended.

The dairy grievance is old and specific. Canada manages milk, poultry and egg production through quotas that cap domestic output and keep prices stable for farmers, and it protects the system with tariffs of more than 200 per cent on imports above set quota volumes. American negotiators have attacked it for decades, and the North American trade agreement that took effect in July 2020 opened only a small slice of the Canadian market. Supply management is politically sacred in Quebec and Ontario, which means no Canadian government can dismantle it quickly under threat.

Untested in court

The legal risk runs both ways. With no case law on Section 338, nobody knows what a court will count as discrimination or how far judges will defer to the president's finding. Importers are likely to sue at the Court of International Trade, and until judges rule, companies must decide whether to pay a 50 per cent duty now in the hope of a refund later.

A tariff on the Great Lakes economy

A 50 per cent tariff on America's biggest trading partner cuts through the tightly linked car, timber and energy industries around the Great Lakes. Canadian lumber, aluminium and part-built car assemblies are effectively priced out of the American market, which will leave American builders short of supplies and paying more to produce.

The car industry shows how the damage compounds. Parts often cross the border several times before a finished vehicle leaves the assembly line, and a duty charged each time a component enters America stacks up well beyond the headline rate. Canadian softwood already faced American anti-dumping and countervailing duties from a dispute that has run for decades, so a further levy lands on builders' costs within weeks. Canada is also the largest foreign supplier of crude to American refineries, and if oil is covered, Midwestern plants set up to process heavy Canadian grades cannot switch supplies overnight.

A few American producers gain, chiefly domestic sawmills and the country's remaining aluminium smelters. The losers are far more numerous: homebuilders, carmakers and their suppliers, and the consumers who pay for all of it. In Canada, which sends about three-quarters of its exports to the United States, the blow falls on Ontario's car plants, British Columbia's forests and Quebec's smelters, and the Canadian dollar is likely to weaken as exporters lose their main market.

The Bank of Canada faces an awkward choice. A tariff that cuts exports weakens growth and argues for lower interest rates, while a weaker Canadian dollar raises import prices and argues for caution, the same dilemma it confronted when American tariffs rose in 2025. Much of the adjustment is likely to come through the currency, which cushions exporters at the cost of dearer imports for Canadian households.

Ottawa's record of retaliation

Canada has a long habit of hitting back. When Smoot-Hawley passed in 1930, Ottawa was among the first to raise duties on American goods, and when Washington imposed steel and aluminium tariffs in 2018 and broader tariffs in 2025, Canada answered with counter-tariffs aimed at American products. A 50 per cent levy leaves any Canadian government little political room to do otherwise.

The case for a short-lived tariff is that it may be a bargaining position more than a policy. A rate this high on the closest ally invites exemptions, court challenges and lobbying from American industries, and Ottawa could offer concessions on digital taxes to get it lifted. There is precedent for a quick retreat: the steel and aluminium tariffs Washington imposed on Canada in 2018 were lifted in May 2019, clearing the way for the new continental trade agreement to be ratified. That deal came after a year of retaliation, and the cost to firms on both sides of the border was paid in full before the tariffs were removed. Even a brief tariff disrupts contracts and inventories, though, and the uncertainty alone discourages cross-border investment.

The signals to watch are Canada's retaliation list, filings at the Court of International Trade, lumber and aluminium prices and any exemptions for car parts. If the 50 per cent tariff stands, American builders and carmakers will probably face shortages and higher costs within months, and Canada is likely to retaliate, putting the continent's shared supply chains at real risk.