The cancellations, which began around 6:30 a.m. ET, involve multiple Air Canada flights out of Terminal One, and may affect other airlines as well, airport officials said.
"Due to a labour disruption between the airlines and their fuelling company, there may be some delays and cancellations today," airport officials said in a tweet.
Air Canada passengers affected by the cancellations of at least 65 flights can find more information here.
An Air Canada official said passengers could rebook at no cost.
Pearson officials are urging travellers to check on the status of their flights before heading to the airport.
The cancelled flights included planes bound for:
- Abbotsford, B.C.
- St. John's.