The tapes, showing construction bosses from the Montreal area and members and associates of the Rizzuto clan, were played for the public during the province's anti-corruption inquiry Wednesday.
"As a citizen and as mayor of Montreal, I was profoundly shocked," Tremblay told reporters Thursday.
"I think that we should have had access to that information a long time ago. The City of Montreal has collaborated with the Montreal police for years. So all of these allegations we've heard were known. And when you see them on television, we ask how is that that we didn't move more quickly."
He said if the city was made aware in 2004, he would have taken stronger measures to restrict certain companies from getting public contracts.
Tremblay is asking the national assembly to convene as soon as possible and consider emergency measures to give the city more power to choose who wins municipal contracts.
He wants to see Bill 35, the provincial law that restricts who is eligible to bid on public contracts, amended as soon as possible, he said.
'He is a muppet!'
City Hall opposition leaders didn't take to Tremblay's avowal that he was shocked by Wednesday's revelations.
Louise Harel, head of the main opposition party, Vision Montreal, said the mayor should have known there was rampant collusion in Montreal's tendering process. Opposition parties tried several times to take steps to counter the problem, she said.
"The mayor of Montreal is looking for excuses to pretend that he didn't know there were problems with mafia infiltration at certain construction entrepreneurs in Montreal," Harel said.
Projet Montréal leader Richard Bergeron had even sharper words for the mayor, saying Tremblay has been in the pocket all along of his former executive council president and right-hand man, Frank Zampino, who was charged with fraud and breach of trust in relation to a public contract.
"He's not naïve. No, I don't believe that. I don't believe that," Bergeron said.
"In fact, this guy has been there for the last 11 years, he has never been the mayor of Montreal. He has been a muppet in the hands of Frank Zampino, of Tony Accurso and so on. He is a muppet!”
Tapes part of Operation Colisée
The videos shown at the Charbonneau commission Wednesday were shot during Operation Colisée, a five-year investigation that culminated with mass arrests in 2006 in the largest sweep against the Italian Mafia in Canadian history.
But the RCMP says it never used the evidence gathered on the videos — because it wasn't pertinent to its drug investigation. The Mounties fought in court, unsuccessfully, to keep from sharing the evidence at the public inquiry.
The Charbonneau commission continued Thursday with further testimony from a Montreal police officer who reviewed the tapes and explained key players. That was followed by stunning revelations in testimony from former Infrabec vice-president Lino Zambito, who admitted that a dozen construction companies conspired to divvy up City of Montreal contracts for sewer and water-main work and to inflate prices.