Ex-Laval mayor Gilles Vaillancourt, former construction boss Tony Accurso and other co-accused piled into the largest room available at the Laval courthouse where the inquiry will take place.
Four men have chosen to go straight to trial in June, while the others opted to go ahead with the eight-week hearing to determine whether they'll stand trial.
Some of the accused were absent without cause Tuesday, while others were granted exemptions that allowed them to be represented by their lawyer for the duration of the hearing.
The presence of so many co-accused along with nearly 40 lawyers made for cramped quarters, leaving reporters sitting in the jury box.
Vaillancourt quit politics in November 2012 after an uncontested reign of 23 years as Laval mayor.
He was among 37 people arrested in May 2013 by Quebec's anti-corruption unit. One of the co-accused has since passed away.
Vaillancourt, former city manager Claude Deguise and ex-city engineer Claude Asselin also face gangsterism charges in addition to the conspiracy, fraud and corruption charges faced by the group as a whole.
The evidence being presented is under a publication ban.