The Quebec Federation of Labour is seeking a permanent injunction to force Air Canada to conduct all of its heavy maintenance of its fleet in the country.
The union filed a request Friday with the Quebec Superior Court calling on the airline to respect its obligations under the 1988 Air Canada Public Participation Act to maintain heavy maintenance aircraft operations in Quebec.
The act also applies to Ontario and Manitoba.
The provincial government had launched a lawsuit against Air Canada after Aveos Fleet Performance, which carried out much of Air Canada's aircraft maintenance, closed in 2012 in a move that laid off 2,600 employees, including about 1,700 in Montreal.
But the government agreed to drop its lawsuit last month after the Montreal-based company signed a letter of intent to purchase up to 75 Bombardier CSeries planes.
As part of that deal, Air Canada agreed to have heavy maintenance work on the planes carried out in Quebec for a minimum of 20 years, beginning in 2019, but other maintenance work would continue in various parts of Canada along with places like Hong Kong, Singapore and Israel.
Transport Minister Marc Garneau has said the end of the lawsuit would allow the federal government to "clarify" the Air Canada Public Participation Act to avoid future litigation.