The US is banning Canadian products, including alcohol, dairy and motor vehicles, as Canadian retaliatory tariffs on American goods come into force.
In a series of executive orders on Tuesday, US President Donald Trump wrote that Canada is "discriminating" against the commerce of the United States, and ordered the import ban, which will begin 29 September.
Earlier on Tuesday, Canada Prime Minister Mark Carney said in a video address that his country's pivot away from the US as its largest trading partner "will come at a cost".
Both US and Canadian officials have said they would like to strike a deal, but no new talks have been scheduled since negotiations collapsed in late August.
The US is Canada's largest trading partner - generally more than two-thirds of its total exports go to its neighbour.
The BBC has contacted the office of the Prime Minister of Canada for comment.
Last month, the White House had imposed 50% tariffs on around $20bn (£14.8bn) of Canadian goods after several rounds of talks had broken down.
Those tariffs hit sectors including Canada's furniture and wine industries, as well as sporting and fishing equipment businesses.
Canada responded with dollar-for-dollar retaliatory tariffs on US goods like steel, clothing and furniture. The counter-duties came into effect after midnight on Tuesday.
The import ban announced by Trump in response targets various alcoholic drinks and dairy products like whey, according to a series of White House statements signed by the president on Tuesday.
Canada is "discriminating" against US businesses by restricting the distribution of US goods while not doing the same to such products from other countries, the White House said.
Tension between the two countries have also expanded beyond tariffs.
In August, Trump ordered Lake Ontario to be renamed as Lake America, resulting in uproar from Canadians and some Americans.
Times are so dumb now. I’d almost wager that Canada builds a wall and we pay for it.