The suspects, Francois-Vivier Gagnon, Genevieve Vaillancourt, Vanessa L'Ecuyer and Roxanne Belisle, turned themselves in to authorities Friday.
They appeared in Montreal court via video conference on Saturday to face charges of hoax regarding terrorist activity, which means they were accused of inciting fear of terrorism _ not committing a terrorist act.
The charge carries a maximum sentence of five years in prison.
"The Crown must prove these were actions that would cause fear from the public... that terrorist activities were committed," Robert La Haye, a well-known Quebec criminal lawyer, said in an interview.
"It doesn't mean that they are being charged with committing terrorist activities."
They were also charged with conspiracy and mischief of over $5,000, while Gagnon was charged with possession of a prohibited weapon for a knife.
Smoke bombs were set off at several metro stops at the height of rush hour Thursday morning, forcing the entire subway system to shut down and causing a major headache for commuters.
A merchants' association and a conservative economic think-tank have estimated the incident cost Montreal several million dollars in lost productivity.
The suspects were detained for the weekend and are scheduled to appear in court again on Monday.
Meanwhile, a radical student group, which has been highly critical of the student federations leading the fight against the tuition-fee increases, called for a rally in front of the Montreal courthouse during their appearance.
"It is only through the continuity, expansion and intensification of the movement that we can aspire to a fairer society," the group, called Force etudiante critique, or Critical Students Forces, said in a post on its website.
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