An OPP officer pretended to be a news reporter at a Mohawk protest that prompted the closure of a major rail line and Highway 401 in eastern Ontario during last year's Aboriginal Day of Action, CBC News has learned.

The officer's tactics have emerged from testimony recently made public when a judge overturned a publication ban on the preliminary hearing for Mohawk protester Shawn Brant.

Observers and media organizations, including the CBC, are protesting the tactic of police posing as journalists, saying it makes reporters' jobs more difficult and more dangerous.

Const. Steve Martell testified last August that he pretended to be a journalist on the evening of June 28, 2007, and got so close to the barricades that he recognized some protesters' faces.

"You were acting in an undercover capacity, as you've told us, and you had a video camera," Brant's defence lawyer, Peter Rosenthal, asked him during his appearance in a Napanee, Ont., court.

"What were you pretending to be?"

"I just pretended to be part of the media," Martell replied.

'There's no real guidelines': Martell testifies

Martell told the court it was his idea to pose as a cameraman and he did not discuss the plan with a superior officer.

When Rosenthal asked whether the OPP had any guidelines for undercover officers as to what roles they can or cannot play when they are undercover, Martell testified that officers are instructed only to refrain from illegal activity.

"So, as role-wise, there's no real guidelines," he said.

"But isn't there a concern that if officers pretend to be media, that might interfere with freedom of the press in some sense? Have you ever heard any such concern?" Rosenthal asked.

"No," Martell answered.

Police used tactic at Ipperwash standoff

It is not the first time that OPP officers have posed as journalists. Videotape recorded during an aboriginal occupation of Ipperwash Provincial Park in 1995 shows reporters questioning undercover officers pretending to be a camera crew a day before an OPP sniper shot and killed protester Dudley George.

"You guys shooting for someone?" one of the reporters asks one of the officers.

"Freelancing," he replies.

When asked specifically who he's working for, he tells reporters: "UPA."

"What's it stand for?"

"United Press Associates," the officer replies, but no such organization exists.

When the videotape came to light four years ago, the OPP promised to "revisit" the tactic, but based on evidence presented ahead of Brant's trial, it appears the force has not stopped using it.

Tactic a concern for public: reporters' group

John Miller, a journalism professor at Toronto's Ryerson University, said police posing as reporters is highly disturbing.

"That's going to make it more difficult for legitimate media to get interviews with the people at the centre of a dispute," he told CBC News.

It's not only a matter of concern for the media, but also for the public, said Mary-Agnes Welch, president of the Canadian Association of Journalists.

"They look to us to try to get sort of behind the scenes and have as much access as we can to tell them what's happening," she told CBC News. "And if we can't talk freely to the people we need to talk to, the average person out there won't get the full breadth of the story."

The CAJ is calling on police forces across Canada to stop impersonating journalists. The CBC is also protesting the tactic.

Last year, an officer in Vancouver lured an anti-Olympics protester to his arrest by posing as a reporter.

Brant faces several charges, including mischief, and could be sentenced to up to 12 years in prison if convicted. His trial in Napanee, Ont., is scheduled to begin in January.