Premier Ed Stelmach has instructed his energy minister to investigate accusations that Alberta's Energy and Utilities Board hired private investigators to spy on landowners during hearings.

The order comes after the arm's-length energy regulator admitted to hiring "security personnel" to oversee central Alberta landowners opposed to a proposed 500-kilovolt power line between Calgary and Edmonton.

Energy Minister Mel Knight will find out who made the decision and why to ensure the public's confidence in the board isn't compromised, Stelmach said Tuesday.

The premier said he expects the results of the investigation to be made public soon.

Landowners living near the proposed site of the power line 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 incidents at a public hearing into the project. Afterward, the board decided to accept only written submissions and close the courtroom in the central Alberta town of Rimbey.

Landowners were moved into a nearby recreation centre to watch the proceedings on TV.

Last month, board spokesman Davis Sheremata admitted the energy regulator had hired security officers to keep an eye on the landowners watching the hearings in the recreation centre.