Almost 200 flights were cancelled at Toronto's Pearson International Airport today after workers assigned to fuel aircraft called in sick, joining an unsanctioned job action that has hit Air Canada the hardest.

Consolidated Aviation Fueling Services saw less than half of its expected employees show up for morning and early afternoon shifts at Pearson today.

Those who stayed away are protesting what they say will be future job losses stemming from Air Canada's decision to switch fuel providers.

Airport officials said at 5 p.m. the disruption had caused 185 flight cancellations.

"We have been co-ordinating with the air carriers and have encouraged them to prioritize their flights," Howard Eng, president and CEO of the Greater Toronto Airport Authority, said in a statement.

The cancellations involved multiple Air Canada flights out of Terminal 1 to destinations across the country and parts of the U.S.

Both the union and the GTAA said they do not know whether there will be further disruptions on Saturday. Travellers are advised to check their flights before leaving home.

Airport officials said earlier other airlines may also be affected, though throughout the day the airport's online departure board showed almost all of the cancellations were Air Canada flights.

Local 2413 of the International Association of Machinists and Aerospace Workers, which represents the workers, did not sanction Friday's job action.

Union spokesman Bill Trbovich said earlier in the day that morning crews refused overtime and managers were expected to do the refuelling.

Some 300 fuelling workers at Pearson expect to lose their jobs this October after Air Canada opted to switch providers, according to a union memo.

The workers have been aware of the coming change since last fall, both the union and Air Canada say.

Frustrated passengers who made it to the airport before finding out about the cancellations lined up to rebook flights.

Air Canada offers free rebooking

Air Canada spokesman Peter Fitzpatrick said the airline wasn't directly involved in Friday's dispute.

"This is between the fuelling company employees and the fuelling company. We're a third-party victim," said Peter Fitzpatrick.

"This is not a labour disruption between the airlines and their fuelling company," he said in an email to CBC News.

"This is a labour disruption at Consolidated Aviation Fueling Services which is affecting all airlines at Pearson."

Fitzpatrick confirmed Air Canada had switched providers, but said the airline expects that the fuellers would be able to find work with the new company it has hired.

Air Canada passengers affected by the cancellations can find more information here.

An official for the airline said passengers could rebook at no cost.

Airport officials are urging travellers to check on the status of their flights before heading to the airport.