OTTAWA -- Prime Minister Justin Trudeau is leaving the door open to tighter travel restrictions, including a possible ban on outbound air travel as COVID-19 case counts climb across the country.

"We're always open to strengthening them as necessary," Trudeau said, referring to measures restricting international flights.

Officials are keeping a close eye on countries where more easily transmissible strains of the coronavirus that causes COVID-19 have broken out, he said.

The prime minister pointed to worrisome mutations in Brazil as well as the United Kingdom, whose outbound flights Canada banned in December.

Those flights have been permitted again after government began requiring incoming passengers to present proof of recent negative COVID-19 tests before boarding.

"We will continue to look at various variants, various geographies, and make sure we're taking the right decisions and the right measures to keep Canadians safe," Trudeau said at a press conference at Rideau Hall on Friday.

The choice of whether to bar travel to the United States lies largely with the U.S., not Canada, since the country of arrival has jurisdiction over who enters, he added.

Earlier this month, a survey by Leger and the Association for Canadian Studies found that 87 per cent of respondents said they would support a total ban on international travel until there are several consecutive days of reduced numbers of COVID-19 cases.

Leger vice-president Christian Bourque said the response is consistent with similar questions asked throughout the pandemic, but also reflects a growing desire by Canadians for governments to take tougher action to curb the spread of COVID-19.

That urge comes amid a backlash to provincial and federal politicians travelling to beaches abroad over the holidays.

The prospect of a hard-nosed travel bans raises constitutional questions around freedom of movement.

Section 6 of the Charter of Rights and Freedoms states that "every citizen of Canada has the right to enter, remain in and leave Canada."

All rights are subject to reasonable limits, but can only be reined in when it's "necessary and proportionate," Michael Bryant, executive director of the Canadian Civil Liberties Association, said in an interview.

"While the precautionary principle would suggest that when in doubt keep people home, our constitution demands more than just a when-in-doubt approach for particular activities."

Overseas sojourns shoulder the blame for only a fraction of outbreaks.

Under two per cent of all coronavirus cases reported in Canada stem from foreign travel, according to the Public Health Agency of Canada.

A ban on outbound trips makes little sense to Michael Feder, a Vancouver-based lawyer with expertise in constitutional law.

"It's the coming back that's trouble," he said.

"No one's annoyed that Alberta politicians went to Hawaii. They're annoyed that they went to Hawaii and came back."

The requirement for international passengers to show negative results on a recently conducted COVID-19 test followed by two weeks of self-isolation on home turf amounts to a strong barrier against viral spread. An outright flight ban would do little to bolster that defence, but it would encroach on mobility rights, Feder said.

"I think it's infuriating to see elected leaders taking off for sunnier climates," he said, calling it an "act of hypocrisy."

"But I don't actually see how a restriction on outbound travel does anything to help Canada combat the pandemic."

Trudeau sought to explain the disparity between stringent lockdown measures such as Ontario's stay-at-home order or Quebec's curfew and the open runway on jetting off to a Caribbean all-inclusive.

"Different jurisdictions will set up the rules that they think are best based on the best advice of their public health officials. On the federal side we have discouraged non-essential international travel, including by imposing mandatory quarantines for anyone returning to Canada and now mandatory testing for anyone before they get on a plane to come back to Canada," he said.

The new curtailments prompted airlines to slash flight schedules over the past week, with Air Canada and WestJet announcing 2,700 layoffs.

Air Transat flight numbers have fallen by more than 90 per cent year over year, the company said.

A ban on non-essential travel would mean a total shutdown, at least for a time, said Air Transat spokesman Christophe Hennebelle.

"However 'essential travel' is defined, such a ban would probably mean that we would need to stop our operations entirely, unless specific support is granted to help us maintain some form of connectivity," he said in an email.

This report by The Canadian Press was first published Jan. 15, 2021.