Prime Minister Justin Trudeau announced that Canada is barring entry to all travellers who are not Canadian citizens, permanent residents or Americans.

“I know this news will spark concern among Canadians travelling abroad. I want to assure you that our government will not leave you unsupported,” he said.

“To help asymptomatic Canadians to return home, our government will set up a support program for Canadians who need to get on a plane. Canadian travellers will be able to get financial assistance to help them with the costs of returning home or temporarily covering basic needs while they wait to come back to Canada.”

This expands new measures taken to combat the spread of COVID-19.

Trudeau added that there will be exceptions for air crew, diplomats, immediate family members of citizens and, “at this time,” U.S. citizens.

No one who is displaying symptoms will be permitted to board a flight to Canada, Trudeau continued.

Air operators will be required to complete a basic health assessment of every passenger.

“I know that these measures are far-reaching. They are exceptional circumstances calling for exceptional measures,” he said.

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Calling it “uncharted legal territory,” Michael Bryant, executive director of the Canadian Civil Liberties Association, said barring Canadians from flights home because they exhibit symptoms effectively strips them of their right to re-enter the country. He said the government’s decision could be unconstitutional, and that he would consider mounting a challenge.

“It’s a fundamental right, the idea that you can come home,” he said. “If you’re a Canadian, it’s a fundamental right. You should always be able to come home under any circumstances.”

University of Ottawa constitutional expert Errol Mendes said that, on one hand, one could argue a ban on boarding a flight is justified, rational and proportionate to the threat of passengers and crew contracting the virus.

On the other hand, he said, the symptoms may not be properly assessed by staffers who are not medically trained — which could mean someone being barred from boarding based on the symptoms of some other illness. That could be a “very persuasive position in front of a judge deciding on the ban’s constitutionality,” Mendes said.

Trudeau also said that as of March 18, international flights will be permitted to land only at the international airports in Montreal, Toronto, Calgary and Vancouver, in order to enhance screening. Incoming domestic flights, and those from the U.S., Mexico and the Caribbean and from St. Pierre et Miquelon, can still land at other airports…

Trudeau said the new border controls will not apply to trade and commerce in order to keep Canada’s supply chains open.

An official in the PMO said the measures will be in place “as long as necessary” because the situation is “evolving.”

Deputy Prime Minister Chrystia Freeland said the decision to keep the border open to Americans was made to reflect the integration of the two economies and populations, and to maintain essential supply lines for things like food.

“That border is absolutely vital to the daily lives of the people who live on both sides of that border,” she said.