The crowd gathered and caused several loud disturbances across the campus despite a court granted injunction forbidding protesters from blocking students from going to class.
The university’s administration called Montreal police, who arrived around 2:45 p.m.
At least 21 people have been arrested.
Demonstrators have been disrupting classrooms for the last two days.
At least six classes were cancelled Tuesday after protesters ran in, singing, turning on and off the lights and erasing notes on the professors’ white boards.
After a standoff where teachers reportedly stepped in between students and police, GARDA security officers replaced SPVM police just before 4 p.m.