President Donald Trump signed executive orders on Monday to slap 50-percent tariffs on numerous Canadian goods, accusing Ottawa of unfairly treating American products including alcohol, automobiles and dairy items.
The tariffs will take effect within 30 days and affect a broad range of items such as wine, hockey sticks and cement, according to a White House fact sheet.
Trump invoked Section 338 of the Tariff Act of 1930, a rarely used legal mechanism that lets officials impose duties on countries engaged in discriminatory trade practices.
Energy products, potash and goods already subject to sector-specific tariffs will be exempt from the new duties, the White House said.
The tariffs will, however, hit products covered under the US-Mexico-Canada free trade agreement, marking a significant departure from Trump's previous approach.
Since returning to office last year, Trump has imposed sweeping tariffs on trading partners but typically exempted goods entering the country under the North American free trade pact.
The move threatens to deepen tensions between Washington and Ottawa at a particularly fraught moment.
Trump had threatened Canada with additional tariffs just days earlier, citing smoke from wildfires that crossed into American territory as justification for the escalated trade action.
