Montreal's homeless will have to find new places to sleep or face hefty fines, as the city's downtown borough of Ville Marie bans overnight stays in public squares.

The ban takes effect at 12:01 a.m. Friday, making it an offence to sleep in 15 downtown squares between midnight and 6 a.m.

The penalty is a fine of $141 for a first offence. If offenders can't pay the fine, they face jail time.

Parks are already off-limits to overnight sleeping.

A 27-year-old man who identifies himself only as Bo spent Wednesday night in a popular downtown square, not knowing it was his last legal night to do so.

"If that law starts up tomorrow, that we can't sleep here, that's a real bummer, man," he told CBC News.

Ville Marie borough Mayor Benoît Labonté said the ban is necessary in part because sleeping wasn't the only thing happening in the public spaces.

"There were a lot of problems with … prostitution and drug selling in some parks," he said.

Just wanted a spot to sleep

Many of the city's homeless acknowledge that those activities were taking place.

But Bo said many people like him were there just to sleep.

He worries about what will happen if they have to hide somewhere to settle down for the night, away from a place where others might notice a criminal attack or health problem.

The city suggests shelters are a good alternative.

Earlier this year, as Montreal's summer festival scene ramped up, businesses pressured the city to clear homeless people from the streets, leading to a police ticketing drive.

People loitering, sleeping in parks and panhandling often faced time behind bars because they couldn't pay fines.

On average, about 30 homeless people were being jailed every day, according to a University of Montreal study commissioned by RAPSIM (Réseau d'aide aux personnes seules et itinérantes de Montreal), an advocacy group for the homeless.

Some faced fines of thousands of dollars because they were repeat offenders.