With Montreal's Grand Prix weekend less than a week away, Charest expressed concern that student groups would disrupt the international event, which brings millions of dollars to the province each year.
He said students, who have spent almost four months striking against a proposed tuition hike, should leave Grand Prix fans alone given the financial importance of the race.
The latest round of talks collapsed Thursday afternoon when Charest's education minister, Michelle Courchesne, declared the two sides had reached an "impasse."
Around 10,000 students took to the streets of Montreal that night to decry the government's decision to give up on negotiations. A much smaller crowd did the same in Quebec City.
On Friday, the 39th night of protest through the streets of Montreal was quickly declared illegal by police, who allowed it to proceed as long as protesters didn't resort to violence. A similar demonstration also took place in the provincial capital.
The crowds were boisterous but smaller than on previous nights. Still thousands of marchers were joined at times by cyclists participating in a nighttime bike tour.
The events were peaceful, with demonstrators occasionally lying down in the middle of the road. People cheered and yelled support from the sidewalk and one construction worker banged his hammer on the scaffold in tempo with the pots and pans as the demonstration passed.
Joining the crowds were mascots such as the cartoon character Scooby Doo as well as the Anarchopanda.
At the park where the main nightly march begins, hundreds of people gathered to watch a screening of the Hugo Latulippe documentary "Republique" about the future of Quebec.
"It's all well and good to protest against Jean Charest, to protest against the government," Charest said Friday while visiting a suburb west of Montreal.
"But they're in the process of hurting Quebecers and the people from whom they're seeking support. I think they have to examine their consciences when it comes to their acts.
"If they had a message to get across, I think we can conclude it has been received."
Charest's warning comes at a critical time for the main student groups. One of the most visible, and moderate, leaders stepped down on Friday as his two-year mandate expired.
Leo Bureau-Blouin, who headed an association of college students known as FECQ, will be replaced by 19-year-old Eliane Laberge. Bureau-Blouin had been praised in many circles for his even-handed leadership amid rising tensions.
"I hope that Ms. Laberge can succeed where I failed, that is in finding a solution to the conflict," Bureau-Blouin said Friday.
He also confirmed that the student groups sent two letters urging the government to send the dispute to mediation, but never received a formal response.
A more hardline student association, the CLASSE, has been busy preparing for what it hopes will be a large demonstration in Montreal on Saturday.
It has also invoked the possibility of using the Grand Prix as a platform for the student cause.
Matthew Larose, a 32-year-old construction foreman, says he'll probably be going to the big demonstration like he has seven of the nighttime marches. He's against the tuition increases but also against Law 78.
"If they can do it in Quebec, they can do it everywhere else. It sets a bad precedent for freedom of speech, freedom of assembly, freedom of everything. They're going completely against the Charter of Rights and Freedoms and it's disgraceful."
The government claims one of the group's spokespeople, Gabriel Nadeau-Dubois, threatened during the latest round of negotiations to disrupt the event. Nadeau-Dubois has said the group would not prevent people from going to the race.
At the Thursday night demonstration in Montreal, members of an anti-capitalist group handed out pamphlets calling on demonstrators to make their presence known during Grand Prix weekend.
Charest's Liberal government passed emergency legislation last month aimed at calming student protests, which have at times turned violent.
Student leaders can face stiff fines under the law for supporting illegal demonstrations, and Charest said Friday it is up to student leaders to establish the parameters of their protests.
"These people have the ultimate responsibility and I expect them to assume it totally," Charest said.
The emergency law has been used sparingly. Several of its provisions have been criticized by legal experts and human rights activists, who say they harm such rights as freedom of association.
— With files from Nelson Wyatt and Ross Marowits
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