The operation began at 5 a.m., involving 36 warrants in seven cities including Montreal, Laval and the North and South Shores.
Laval police spokesman Frédéric Jean says officers have made about a dozen arrests so far.
Jean said the investigation called "Projet Souterrain" — or "Project Underground" — is being led by the Laval police’s anti-gang unit.
He said it started with an anonymous tip in September 2013.
“We're looking at breaking up an operation that deals with the distribution and trafficking of synthetic drugs, cocaine and cannabis,” said Jean.
Jean said the trafficking network covers a vast territory that extends from St-Bruno and Candiac on the South Shore, to Blainville and Saint-Jérôme on the North Shore.
The raids involved officers from eight different organizations including Laval Police, the SuretéduQuébec and the RCMP.