The regulator hasn't yet determined the size of the leak near Boyle, Alta., but says there are no public safety concerns.
The line, which carries sweet natural gas, is owned by TransCanada Pipelines Ltd. (TSX:TCA)
A member of the board's emergency response team is on site and the affected portion of pipeline has been shut down.
Local first responders and aboriginal groups are being notified.
The board says it was notified of the leak late Wednesday morning.