India, Aug. 22 -- The United States was set to impose 50% tariffs on $20 billion worth of Canadian products early Saturday after last-ditch negotiations failed to resolve the latest strain in already tense relations between the historic allies.

President Donald Trump's import taxes will hit about 5% of what Canada ships to the United States every year, including products ranging from hockey sticks to tongue depressors.

But the political impact will likely be even bigger than the economic fallout. Canada has threatened to retaliate against any new tariffs with levies of its own, aggravating a trade fight between countries that sold each other $880 billion worth of goods and services last year.

The tariffs were initially supposed to kick...