Nearly 2,400 Montreal blue collar workers including union leadership will face sanctions for leaving work to attend a union meeting last week after they were ordered to remain on the job.

The Canadian Union of Public Employees summoned its members to a special general assembly to discuss upcoming negotiations with the City of Montreal on Dec. 8. The workers' current contract expires in December 2017.

Montreal Mayor Denis Coderre said this morning that the workers chose to take part in an illegal strike and knew there could be consequences.

"I'm sorry, but a contract is a contract," Coderre said. "It's simply not acceptable."

The blue collar workers had already been ordered to show up to work by the Quebec government's essential services council.

In a letter to the city's general manager, the city's labour relations director, Danny Boudreault, recommended suspensions ranging from six days to two months for workers, depending on their role in the decision to leave their jobs for the meeting.

"We recommend severe sanctions to send a clear message to the union that the city will not be intimidated and will not accept illegal actions," the letter reads.

Montreal blue collar workers met at Palais des congrès for a special meeting last week. (Simon-Marc Charron/Radio-Canada)

Four people, including union president Chantal Racette, will face the stiffest punishment: two months suspension without pay.

Racette said she has not yet received formal notice of the sanctions, but will review it with the union's legal team.

She accused Mayor Denis Coderre of attempting to "dismantle the public service."

She said the meetings were not about the worker's current collective agreement, but about the fiscal pact between municipalities and the Quebec government signed earlier this year.

Municipalities have accepted less provincial cash in exchange for more power in contract negotiations with their employees. The province plans to review the negotiation process.

Opposition leader Luc Ferrandez says the city's reaction was too harsh given the relatively small length of time the workers were off the job.

He fears relations with the union will only get worse.

"For sure it will escalate," he said.

"I [hope it won't], but you have to know very little about municipal administration to believe that the cols bleus will just say, 'We're so sorry. We'll go back home for our four days of suspension for 40 minutes of strike,' and that will finish there."

Workers who participated in the illegal work stoppage, but played no part in organizing it, will face six days suspension. Those days won't be served consecutively.

The union, which represents 110,000 members across the province, recently posted a video promising plenty of resistance in upcoming contract negotiations.