Air Canada began canceling flights Thursday ahead of a possible strike by its flight attendants that could impact hundreds of thousands of travelers. A complete shutdown of the country's largest airline threatens to impact about 130,000 people a day.

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.

As of 8:00 pm Friday, the airline said it had cancelled 623 flights affecting more than 100,000 passengers. Its full 700-flight daily schedule has been scrapped for Saturday