Air Canada cancelled hundreds of additional flights on Sunday after the union representing its flight attendants announced the workers would remain on strike in defiance of a back-to-work order. The Canadian Union of Public Employees said it filed a challenge in Federal Court on Sunday to an order by the Canada Industrial Relations Board that said its members must return to work by 2 p.

Air Canada suspended its guidance through the end of this year, citing the impact of a strike by flight attendants that has caused the airline to suspend its flying schedule.