TORONTO -- The Speaker of the Ontario legislature said Tuesday he never felt political interference that would prevent him from making decisions, despite opposition charges that the Liberal government tried to bully him into changing a key ruling.

Newly-released emails show senior Liberals in former premier Dalton McGuinty's office tried to get Speaker Dave Levac to change his preliminary finding that then-energy minister Chris Bentley was in contempt for not releasing all documents on two cancelled gas plants.

The Progressive Conservatives and New Democrats accused the Liberals of trying to pressure Levac into changing his ruling, something they said was "akin to trying to influence a judge on a decision" in a court case.

"That's pretty serious stuff," said NDP house leader Gilles Bisson. "You don't do that. There are ramifications."

However, Levac issued a statement Tuesday saying he's frequently lobbied by members of all three parties on a range of issues, and has never felt undue pressure.

"I have never felt unable to make an informed, objective and procedurally sound decision, free of political interference," Levac said in the statement.

"The fact that the ruling did stand should also speak for itself."

The Conservatives said they wanted the integrity commissioner to find out if the Liberals threatened Levac or made the Speaker an offer to drop the contempt ruling.

"It's absolutely unclear what the threat was or what he was offered or what the demands of him were," said PC energy critic Vic Fedeli.

"I'm looking forward to the integrity commissioner looking into the very integrity of that conversation. What occurred? What was he threatened with?"

The New Democrats plan to call two of the McGuinty staffers whose emails talked about pressuring the Speaker to change his ruling to appear before the justice committee hearings into the cancelled gas plants, which resume next Tuesday.

"The first people we need to hear from are those people who were out there trying to bully the speaker," said New Democrat house leader Gilles Bisson. "What we hear from them will determine if we call the Speaker. If need be, we will call the Speaker."

The Tories said email discussions about trying to intimidate the Speaker show the Liberals will stop at nothing to try and bury the scandal over their decision to cancel gas plants in Oakville and Mississauga prior to the 2011 election, which has cost at least $585 million.

"Operatives, including the senior campaign adviser to Premier Kathleen Wynne, clearly attempted to hijack a Speaker's decision," Fedeli wrote in a letter to integrity commissioner Lynn Morrison.

"Which incentives were offered or punishments were threatened is unclear, but these actions threatened and undermine the institutions we value in our democracy."

The emails between senior Liberals showed Levac had rebuffed attempts by former McGuinty aide Dave Gene, who met with the Speaker in an effort to convince him to change the contempt ruling.

McGuinty resigned as premier last September and prorogued the legislature just hours before the committee hearings were to begin into the cancelled gas plants, delaying the inquiry for several months.

Meanwhile, The Canadian Press has learned that the Wynne government has retained the services of a prominent defence lawyer to help deal with the OPP investigation into allegations that senior McGuinty aides deleted emails on the gas plants.

A source familiar with the topic said Bill Trudell -- chairman of the Canadian Council of Criminal Defence Lawyers -- would act on behalf of the Liberal aides as a facilitator.

"Mr. Trudell has been retained to ensure that current staff members, who may be contacted (by police), are aware of their obligations and responsibilities, and work together with the OPP to facilitate their investigation," the source said.

Provincial police began their criminal investigation last month after the Tories complained about the destruction of emails by senior Liberal staff.

Their complaint came after Privacy Commissioner Ann Cavoukian reported that top Liberals in McGuinty's office had deleted the emails and tried as late as this past January to permanently wipe email accounts from government databases.