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.

A leader of the union on strike against Air Canada (AC.TO) said on Monday he would risk jail time rather than allow cabin crews to be forced back to work by a federal labor board, raising the stakes ...

The strike stranded more than 100,000 travelers around the world during the peak summer travel season.