Chris Lewis was sworn in Tuesday as commissioner of the Ontario Provincial Police. (Darren Calabrese/CP)

Ontario's new police commissioner says it's against police policy for officers to pretend to be journalists to gather evidence on suspects, but he can't rule out that it could happen again.

Chris Lewis said it would happen only in "rare" cases where public safety is an issue.

"To save a life, to get close to that person, then we might do what we have to do," Lewis said Tuesday as he officially took over as Ontario Provincial Police commissioner from the retiring Julian Fantino.

Media advocates are launching a court action this fall against the practice, saying it undermines the public's trust in reporters.

At first, Lewis said his officers would no longer pose as reporters, citing a policy brought in three years ago that stopped the practice. But he quickly added that he couldn't rule out "every exigency in the world," and said exceptions could arise.

In 2007, an OPP officer pretended to be a journalist at a Mohawk rally. More recently, an officer posed as a reporter to gather evidence from a convict in a prison.

In Quebec, three provincial police officers posed as protesters at the summit of the three North American leaders at Montebello in August 2007.

Canadian Journalists for Free Expression, a media advocacy group, said it is aware of a handful of cases in Ontario, but called them the tip of the iceberg. Police across Canada employ the tactic, Arnold Amber, CJFE's president, said in an interview Tuesday.

"We understand that the Mounties do it, the OPP does it, the Quebec police do it," said Amber. "Every way you look at this here, it is a lousy practice."

The CBC, CJFE and RTNDA Canada plan to launch the legal challenge in Ontario Superior Court against the OPP and the Ministry of Community Safety and Correctional Services.

Consequences for truth

Sources may not talk to reporters if they think they might really be speaking to a police officer, so important stories might not get told, said CJFE manager Julie Payne.

Pedophile priests at the Mount Cashel orphanage and the Robert Pickton serial killings are two cases in which police investigations were launched only after stories appeared in the news media.

The most recent report of an Ontario Provincial Police officer posing as a reporter emerged last weekend. The officer gathered evidence against Phillip Vince in the July 1999 cyanide poisoning of fellow inmate Scott Barnett at Millhaven Penitentiary in Kingston, Ont.

"You had a police officer pretending to be a journalist who was going to write about this prison inmate, in order to get him to potentially give evidence of a crime he had committed," said Payne. "And the police officer, as that journalist, made all sorts of promises that the conversations were to have journalist's privilege and wouldn't be shared with police."

Vince, 52, was arrested at the Saskatchewan Penitentiary in March and charged with first-degree murder. He had been serving a life sentence for two first-degree murders in Durham Region in 1985.

Canadian Journalists for Free Expression asked police previously to stop the practice. The group sent a letter in July 2008 to Ontario's minister of community safety requesting that the investigative tactic be eliminated.