MONTREAL -- Masks are soon going to be mandatory in all of Montreal's indoor spaces that are open to the public.

Mayor Valérie Plante announced the move on Monday afternoon on her Twitter and Facebook accounts, saying the city is working on a new bylaw and aims to put it into effect by July 27.

"Over the past few days, we have witnessed the emergence of some outbreaks in the suburbs of Montreal, which could undermine the efforts we have been making since the beginning of this pandemic," said the Facebook statement.

Plante said the new rule will apply to "enclosed public places" and that the city will "draw on the experiences of Canadian cities that have already adopted such a bylaw or are about to do so."

There will be a grace period to allow for people to adjust and become educated, though Plante said "we will not hesitate to crack down on offenders in the long run."

Currently in Montreal, masks are only mandatory in one suburb, Cote-Saint-Luc, where the rule went into effect last week. They will become mandatory on public transit on July 13, though there will then be a two-week grace period, and enforcement will also begin July 27.

Other Canadian cities have also moved recently to make masks mandatory, though with shorter delays. On Monday, the City of Ottawa announced that masks will be required as of 12:01 a.m. Tuesday, just a few hours later.

Toronto announced on June 30 that it was giving about a week's notice before masks would become mandatory starting July 7, the same day as Ottawa.

Plante told CTV News that lining up Montreal's start date with its previously announced public transit rule would simplify the education campaign. She also needed time to organize the logistics, she said.

“It takes a bit of time to create a bylaw, and we also needed to unite the city council for that," she said.

New research has bolstered the argument for mask-wearing. One study published in June showed, by comparing infection rates before and after various mask laws went into effect, that masks have already saved thousands of lives around the world.

Plante said the local move had been encouraged by Montreal business owners.

“The past few days, I’ve been in the field actually talking to restaurant owners and bars and business owners,” she told CTV.

“One thing that came out very clearly is they want this to be mandatory for their own security, for the security of their employees, but also to prevent any kind of new [outbreak].”

Plante said in her statement that health-care workers' health is also at stake. A COVID-19 setback, she wrote, "would be a disaster for human lives and for our economy."

She added in the interview that she was paying close attention to other "big metropolises" like New York and was aware that a second wave among a big population would be very worrisome.

"Especially knowing that Montreal was the epicentre," she said in her interview, "and with all the sacrifices that we have been [making], I just want to minimize all the possible chances of another outbreak here in Montreal."

Caroline Tessier, the director of an association of Montreal commercial development groups, said the local businesses she represents have indeed been wanting mandatory masks, though with a few caveats.

"We are in favour of these new measures, particularly for the retail sector," said Tessier. "This will reassure merchants, but also, and above all, customers."

She said she hoped there would be some fine-tuning of the rules when it comes to indoor dining, however, saying that her association hopes masks will be mandatory when moving around the restaurant for any reason, but that they could be removed when clients return to their assigned place.

"We must ensure that...these places remain attractive to customers and that this sector does not suffer from additional losses," she said.

Plante said she really wants to see Montrealers immediately begin wearing masks voluntarily, and that was why she made the announcement now, before having more details.

"I wanted to send a strong message to Montrealers that we don't have to wait for the bylaw to come out," she said.

"We've done a great job, but we cannot put our guards down."