MONTREAL - Protester threats in Montreal have forced organizers of the Canadian Grand Prix to cancel the free opening day of the event.

Formula One fans were to have had access to Circuit Gilles-Villeneuve at the open house event Thursday. Instead the event was scrapped due to security concerns.

Francois Dumontier, president of the Canadian GP, said in a statement Sunday that organizers had no choice in the cancellation.

"Considering the various disruption threats made public recently, the free admission and the naturally openness character of the open house day, revealed some risks that we could not neglect," said Dumontier.

"Under these circumstances, cancelling the 'Open House' day was the only action we could take. Unfortunately, for the fans and our spectators, it was impossible to escape from such responsibility."

The student group CLASSE has suggested the race could be used as a platform for the demonstrations over tuition fees. On Saturday, group spokesman Gabriel Nadeau-Dubois said it would use the event as a forum to raise its grievances with the province, but wouldn't prevent people from going to the race.

Martine Desjardins, the head of a more moderate student association, said Sunday the threat to the Grand Prix was exaggerated.

"I don't think this was a real threat," Desjardins said, adding that the Quebec government has blown the issue out of proportion to "discredit the student movement."

An anti-capitalist group known as CLAC has also promised to hold disruptive demonstrations leading up to the race. The group handed out pamphlets at recent late-night marches encouraging participation.

Protests over university tuition increases and a new emergency law have caused major traffic headaches and hurt downtown businesses over the past several months. There has been a march every night in Montreal for the past 40 consecutive days.

The Grand Prix isn't the only event concerned about security issues.

The head of the city's Just for Laughs festival also announced he wanted to meet with student leaders early this week to avoid any problems.

Quebec Premier Jean Charest in turn has been critical of threats toward the race that generates an estimated $100 million in revenue for the city. More than 300,000 spectators are expected to attend the June 8-10 event.

An online activist group has also targeted the race.

Anonymous is being investigated by Montreal police for an email threat sent to more than 100 people with tickets to the June 10 race. The group also hacked into a website selling tickets with personal information on buyers, including names, phone numbers, email address and ticket details.