The planned 280,000-square-metre shopping centre would be built near where the Decarie Expressway meets Highway 40.
The Town of Mount Royal supports the project, which would include stores, restaurants, movie theatres and a concert hall. TMR council has already passed several zoning by-laws to help pave the way for building to begin later this year.
But Projet Montréal leader LucFerrandez said he will do everything in his power to make sure the project never goes ahead.
Ferrandez said the island already has too many restaurants, stores and theatres.
He said the new mall would take business away from commercial streets such as St-Laurent Boulevard, Mont-Royal Avenue, and St-Hubert Street.
Ferrandez said it's not clear if the City of Montreal has the power to block the project, but he said he'll try to make his case to TMR's mayor, the people who live there and the developer.
Montreal Mayor Denis Coderre and Russell Copeman, the mayor of the borough of Côte-des-Neiges—Notre-Dame-de-Grâce
have both expressed reservations about the project.
Coderre said on Twitter he would need to hear more about the project's economic impact before giving it his support.
The developer is expected to present its final project design to TMR council in the spring.