It was a difficult day for the Charbonneau Commission, as charges of bad faith and internal bickering brought work to a virtual standstill.

Star witness Martin Dumont, whose testimony this fall may have led to former mayor Gerald Tremblay’s resignation, admitted Monday he lied to the corruption commission over what might have happened at Union Montreal headquarters.

Facing possible perjury charges, former Union Montreal organizer Dumont hired lawyer Suzanne Gagné to challenge the commission.

She argued her client's constitutional rights were violated when Dumont was cornered by investigators.

The charge triggered an ugly exchange between Justice France Charbonneau and Gagné.

“Are you telling me that I'm not being fair with you?” said Charbonneau.

“I'm simply trying to ask you to let me respond,” said Gagné.

Tension mounted quickly, as Charbonneau asked Gagné to lower her voice, to which Gagné agreed.

Charbonneau cut the discussion short, and said Dumont admitted to lying -- and that's all she needed to know.

“The discussion is ending right here, are we clear?” she said.

Gagné, however, told Charbonneau she'd be heading to Superior Court to prevent her commission from further questioning Dumont.

“I have a mandate to request a second opinion from the Superior Court,” said Gagné, who is essentially asking the Superior Court to overrule a decision from the commission.

If she wins, it could severely limit the power of the Charbonneau Commission.

Charbonneau has also hit another snag: a publication ban.

Frank Zampino, the former president of Montreal's executive committee, is awaiting trial on corruption charges.

With a Surete du Quebec investigator about to testify before the commission, Zampino's lawyer Claude-Armand Sheppard successfully requested the ban, arguing it was needed to protect his client's right to a fair trial.