The union for 10,000 striking Air Canada flight attendants said Monday they won’t return to work even though the strike, now in its third day, has been declared illegal.

A labor relations board declared a strike by Air Canada’s 10,000 flight attendants illegal on Monday and ordered their union to tell them to return to work by midday.

The airline has warned that some flights would be cancelled over the next seven to 10 days and said that it "deeply regrets" customer inconvenience.