Alberta's Energy and Utilities Board has admitted to hiring plainclothes "security personnel" to watch over hearings into a proposed 500-kilovolt power line between Calgary and Edmonton.

Last week, landowners fighting the power line accused the board of hiring private investigators to spy on them.

On Monday, board spokesman Davis Sheremata admitted the energy regulator had hired security officers to keep an eye on landowners watching the hearings on a closed-circuit television in a recreation centre in the central Alberta town of Rimbey.

"The security personnel at the Rimbey recreation centre were there to explicitly observe the proceedings and ensure people's safety. That's the duty they were charged with and that's what they were there to do – that is all," he said.

Sheremata said they hired the officers after completing a threat assessment.

Alberta's Energy and Utilities Board is considering a controversial proposal from AltaLink to build a 500-kilovolt power line between Calgary and Edmonton.

Landowners living near the site are concerned about possible health effects and have complained that the board has already decided to approve it.

In April, board staff said they were physically threatened in three separate incidents at a public hearing into the project. Afterward, the board decided to accept only written submissions and close the courtroom. Landowners were moved into a recreation centre near the courtroom to watch the proceedings on TV.

Denied a motion to cross-examine the security officers, the landowners' lawyers are arguing that their lawyer-client privilege was breached by the "private investigators" and are calling for the hearings to be restarted.

"I have observed the individuals … on several occasions to take interest in and/or intrude into solicitor and client discussions," wrote Julian Bodnar, a lawyer for several of the landowners, in an affidavit.

Sheremata said the hearings will continue as planned.

"We are now in the fifth week of cross-examination of the applicants. We are a very long way into this hearing and we have heard a lot of relevant evidence. There is no question that this has been contentious at times, but the hearing is going on."

Alberta Liberal energy critic Hugh MacDonald is calling on the Energy Ministry to disclose the mandate of the security officers and how much money was paid to the consulting company.

"I have met with many of these individuals who are opposed to the transmission line and I certainly wouldn't consider them a security threat. For the most part they're law abiding and they feel very frustrated with this regulatory approvals process to date."