Open this photo in gallery Canadian and American flags fly near the Ambassador Bridge in Windsor, Ont., on March 21, 2020. U.S. President Donald Trump is vowing to stop the export of vital medical supplies despite a warning from Prime Minister Justin Trudeau to keep the Canada-U.S. border open. Rob Gurdebeke/The Canadian Press

U.S. President Donald Trump is vowing to stop the export of vital medical supplies despite a warning from Prime Minister Justin Trudeau to keep the Canada-U.S. border open to goods needed to fight the coronavirus pandemic.

At the White House on Friday, Mr. Trump said he would use the Defense Production Act to prevent U.S. companies from selling N95 respirators, surgical masks, gloves and other personal protective equipment to other countries.

“We need these items immediately for domestic use. We have to have them,” the President said at his daily briefing, describing medical supply exporters as “unscrupulous actors and profiteers.”

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In an executive order, Mr. Trump gave the Federal Emergency Management Agency the power to “allocate to domestic use” several types of medical personal protective equipment that would otherwise be exported. “It is the policy of the United States to prevent domestic brokers, distributors, and other intermediaries from diverting such material overseas,” the order reads.

Update: Canada won’t retaliate against U.S. ban on medical supplies exports: PM

Mr. Trump shrugged off the warning from Mr. Trudeau, as well as criticism from medical manufacturer 3M, which said the U.S. government had ordered it to stop sending N95s to Canada and Latin America.

“I don’t blame them," the President said. "They can push back if they want. We’re not happy with 3M.”

Later in the briefing, Mr. Trump seemed to soften his position, saying that “long-term orders” from other countries to U.S. companies could go ahead. He did not explain the apparent contradiction. “If they have long-term orders and they’re in there. ... I’m not going to be stopping that,” he said.

The executive order also appears to contain some discretion for FEMA, telling the agency to stop exports “as appropriate,” rather than containing an absolute block on exports.

Earlier in the day, Mr. Trudeau said blocking trade to Canada could “end up hurting Americans as much as it hurts anybody else.”

“The level of integration between our economies goes both ways across the border," he said. "We are receiving essential supplies from the United States, but the United States also receives essential supplies and products – and indeed, health-care professionals – from Canada every single day. It would be a mistake to create blockages or reduce the amount of back-and-forth trade in essential goods and services, including medical goods, across our border.”

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Mr. Trudeau and Deputy Prime Minister Chrystia Freeland were vague when asked about retaliation, but both said many Canadian doctors and nurses in southern Ontario work at medical facilities in the Detroit area.

U.S. manufacturers also rely on Canada to supply pulp that goes into manufacturing some of the same surgical masks and gowns Mr. Trump is now vowing to stop exporting. The president of the Harmac Pacific paper mill in Nanaimo, B.C., said one of his U.S. customers doubled orders because of the pandemic, and some of those supplies would normally make their way back to Canada.

Ms. Freeland also referred to Canada’s stand during talks to renegotiate the North American free-trade agreement, in which the country imposed retaliatory measures in response to U.S. tariffs on steel and aluminum.

“I do want to assure Canadians that our government – as has been demonstrated by our action – is prepared to do whatever it takes to defend the national interest. We showed that during the NAFTA negotiations, and, of course, that is the approach that we are continuing to take in this fight against the coronavirus,” Ms. Freeland said, adding that Canada is still trying to secure supplies from 3M and other from countries around the world.

Ontario Premier Doug Ford raised the issue in a phone call with U.S. Trade Representative Robert Lighthizer.

“I can’t stress how disappointed I am with President Trump for making this decision," Mr. Ford told reporters.

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Like Quebec Premier François Legault, Mr. Ford said it is important for provinces to be self-sufficient when it comes to medical equipment.

"I’m not going to rely on President Trump, I’m not not going to rely on any prime minister or president or any other country ever again,” he said.

Prime Minister Justin Trudeau says he will soon be able to give Canadians a better sense of the impact COVID-19 is going to have on this country but he isn’t able to do it yet. The Canadian Press

Mr. Trump on Thursday invoked the Defense Production Act to force Minnesota-based 3M to give priority to orders for N95s that come from the FEMA. In a statement on Friday morning, the company said the Trump government was also trying to stop 3M from exporting the respirators.

“The administration also requested that 3M cease exporting respirators that we currently manufacture in the United States to the Canadian and Latin American markets. There are, however, significant humanitarian implications of ceasing respirator supplies to health care workers in Canada and Latin America, where we are a critical supplier of respirators,” 3M said.

The company warned that, if other countries retaliate, “the net number of respirators being made available to the United States would actually decrease.”

The dispute began as Canada announced it had ratified the new NAFTA deal with the United States and Mexico. The three countries still have to determine when it will take effect.

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It was not immediately clear whether the Trump administration told any other companies to stop exporting. Out of six companies named in a separate presidential order meant to make it easier for the companies to manufacture ventilators, five – General Electric Co., Hill-Rom Services Inc., Medtronic plc, ResMed and RoyalPhilips – indicated they were still doing exports. Vyaire Medical Inc. did not respond to requests for comment.

Editor’s note: A previous version of this story incorrectly said Harmac Pacific in Nanaimo, B.C., is the only producer in the world to make pulp used in hospital gowns and masks. In fact, it is the sole supplier of a specific type of pulp used by some U.S manufacturers of those products.

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