The Canada Industrial Relations Board has declared a strike by 10,000 Air Canada flight attendants illegal and ordered them back on the job after they ignored an earlier order to return to work and submit to arbitration.

A strike by 10,000 Air Canada flight attendants has been deemed illegal, and workers ordered back on the job. The ruling from the Canada Industrial Relations Board comes after the flight attendants defied an earlier return-to-work order that also told them to submit to arbitration.

Air Canada withdrew its financial targets for the year as a strike by flight attendants entered its third day, forcing the country’s largest airline to cancel about 500,000 flights.