A spokesman for the Canadian Union of Public Employees said the airline, the country's largest, was training replacement workers after the flight attendants rejected a tentative contract in August. The union has filed a grievance with the company and Canada Industrial Relations Board.
Air Canada would not comment directly on the grievance or any training. A spokesman said the airline has contingency plans in place "for a wide range of eventualities."
A strike vote wraps up on Tuesday afternoon, with results expected to be announced later that day.
The tentative deal would have sent the issue of pension benefits for new employees to binding arbitration, the union said in August, in a compromise similar to one that ended a June strike by the airline's check-in and call-centre staff.