Conservative Leader Stephen Harper's top communications official should stand down until his role in the appointment of a new head of the Montreal Port Authority is cleared up, two federal party leaders say.

Dimitri Soudas has denied trying to influence the appointment, other than to express the federal government's preference for Robert Abdallah as the port's new chief executive.

Soudas came under renewed pressure Thursday after reports surfaced of an audio recording on YouTube in which purported Quebec businessmen discuss the appointment and Soudas's name is heard.

Soudas's involvement in the appointment in 2007 was raised this week after a joint investigation by Radio-Canada and the Globe and Mail. He and Harper have confirmed that Abdallah was the Conservative government's choice, but in end, the appointment went to Patrice Pelletier.

"Mr. Harper has a duty to tell people what really happened with that case, and he has until May 2 to do so," Bloc Québécois Leader Gilles Duceppe said. "But meanwhile, [Soudas] should step out of the campaign and out of the job."

Liberal Leader Michael Ignatieff told a news conference the latest allegations surrounding Soudas are a part of a larger trend of problems facing members of Harper's inner circle.

"There is a pattern here folks. There is a pattern, we have [former Harper adviser Bruce] Carson, we have four people accused of election fraud, we have Soudas possibly not telling the truth to a parliamentary committee," Ignatieff said in Montreal.

The Liberal leader was clear on Soudas's future: "He's got to go."

NDP Leader Jack Layton also stepped into the fray in Toronto, calling for an investigation.

Harper said on Thursday the allegations against Soudas are "categorically false."

Soudas, speaking with reporters in St. John's Thursday, adamantly denied the allegations.

"We've been clear on this issue," Soudas said. "The government expressed a preference for a particular candidate, so did the City of Montreal, and ultimately the board chose somebody else.

"Now people pretending, or people having discussions, that is their business —  but at no point in time did anybody contact the federal government or me and make such an insinuation. It is absolutely ridiculous."

Asked by a reporter if he had turned down money at any point related to the appointment, Soudas replied:

"Never! And had I ever received anything of that sort, I would have immediately turned it over to the authorities. Never. Anything is always declared. Never, ever, ever .…

"If anybody at any point in time attempts to influence anybody in the Prime Minister's Office, myself included, there will be serious problems."

Duceppe demanded Harper answer questions about Soudas's role.

"I'm asking who is 'the big boss' [of Quebec]?" Duceppe said, referring to an unexplained phrase on the recordings. "Is it Stephen Harper, the one who approved the political meddling by Dimitri Soudas? The leader of the Conservative party has to answer these questions."

The Port of Montreal's board of directors began the process of choosing a new president at the end of 2006, when Dominic Taddeo announced his intention to retire after 23 years as the president of the port.

Under the Canada Marine Act, the seven-person board must act in the best interest of the Port of Montreal.

The board is made up of four people named by users of the port; three others are named respectively by the federal, provincial and municipal governments.