Five pilots have complained that someone on the ground flashed laser beams into the cockpits of their planes while they were trying to land at Toronto's Pearson International Airport.
Two of the aircraft involved were passenger planes, Transport Canada said Wednesday.
The pilots have said they think the incidents are a growing safety issue. Laser beams were aimed at the cockpit window and flashed the pilots in the eye.
Captain Stephen Guetta, a spokesman for the Air Canada Pilots Association, said Wednesday shining a laser at a plane may be seen as a prank, but it could easily become a disaster.
Under certain conditions, he said, it could distract or temporarily blind a pilot.
For example, if such a prank occurred during a night landing in winter, when there is already limited visibility, it could be dangerous, Guetta said.
"It has a potential impact to health and safety of the crew and henceforth the safety of passengers."
Transport Canada said it has received at least 33 reports of bright lights shining into cockpits from the ground over the past two years in Canada.
Eleven of those incidents were in Ontario, of which five were at Pearson.
Peel Regional Police, which is responsible for Pearson airport, said it was not aware of any of the incidents.