The disgruntled workers are among more than 2,000 employees laid off over the weekend by Aveos Fleet Performance.
The protesters are not allowing Air Canada staff to enter a building near Montreal's Pierre Elliott Trudeau International Airport.
Police officers are on the scene, but are not forcing the Aveos employees to leave.
A few kilometres away, another group of laid-off workers is blocking an Aveos building.
Aveos announced Sunday it is shuttering three plants in Montreal, Winnipeg and Vancouver.
Of the 2,400 workers who have been laid off, three-quarters are in Montreal.
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