Canadian Union of Public Employees, or CUPE, which represents the flight attendants, refused to voluntarily submit to arbitration. “The appropriate course of action is for Air Canada to return to the table and resume good faith bargaining,” it said in a statement.

Their union says one of its core demands, to receive pay for groundwork, is unlikely to be introduced in arbitration. The airline began canceling flights ahead of the potential strike.

Flight attendants are demanding better wages and compensation for unpaid work. Currently, Air Canada only compensates flight attendants for the time they are in the air, but its attendants are seeking pay for the work they do before take-off and after landing, too.