MONTREAL—The Montreal police say they wanted to send a strong message during a student demonstration on Tuesday night: the rules of the game have changed.

Of 60 protesters walking against traffic on St-Laurent Blvd. Tuesday night, 45 were corralled and arrested, released hours later with $637 fines.

“I’m not going to share our tactics, but we sent a strong message last Friday and yesterday. Enough is enough,” said Montreal police spokesman Ian Lafreniere.

After nearly a year where municipal bylaw P-6 was half-heartedly enforced, the controversial law was applied in full force on Tuesday. P-6 forbids the wearing of masks during protests and requires that groups provide a planned route to police.

The law was passed by city council last May during a time when student protests were marching nightly through downtown Montreal.

During Friday’s anti-police brutality demonstration, P-6 was also quickly applied, leading to clashes between heavily-armoured riot police and protesters. In the morning before that protest, police officers carried out a number of "preventative arrests" of suspected ringleaders. The suspects were apprehended under an existing warrant.

By the end of Friday’s protest, two groups were corralled and nearly 250 people were detained and ticketed.

“This is not a normal protest, it has a bad history,” Lafreniere explained on Friday evening, following the demonstration. “For the past 15 years this protest has almost always turned bad with riots and mass arrests.”

While coy with details, the police spokesman confirmed Friday's response was characteristic of a new strategy.

“We established last week that it is possible to do a protest in Montreal without breaking anything, but you need to follow all the rules. If you don’t do that, you’ll receive a ticket and that’s what happened.”

In previous protests, the police allowed marches to continue despite labelling them illegal, only carrying out arrests when violence erupted. During Tuesday’s demonstration, protesters disregarded an order to walk in the same direction as traffic, a request disregarded during nearly a year of student unrest. The corralling happened soon after.

“Montrealers are extremely patient, but people should respect the rules,” said Lafreniere. “That includes providing an itinerary.”

The police have made attempts to ensure that groups understand the new rules. Lafreniere confirmed that the force tried to contact organizations to remind them to provide an itinerary before Friday’s protest.

“We sent letters and if you look on social media, they laughed at it, they made a joke of it,” said Lafreniere. “Prior to the protest we also had loudspeakers and contacted people in the crowd who looked like leaders.

“Montrealers have no patience for violence.”