Air Canada suspended plans to restart operations on Sunday after the union representing 10,000 flight attendants said it will defy a government order to return to work. The Canada Industrial Relations Board had ordered employees back to work by 2pm Sunday, and Air Canada then said it planned to resume flights Sunday evening. But the union responded by saying it will challenge the order as unconstitutional, the AP reports. "Our members are not going back to work," said President Mark Hancock of the Canadian Union of Public Employees outside Toronto's Pearson International Airport. "We are saying no." Canada's largest airline now says it will resume flights Monday evening. The backdrop: