Air Canada has suspended plans to restart operations after the union representing 10,000 flight attendants decided to defy a return-to-work order.

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.

Roughly 10,000 Air Canada flight attendants have refused a government order to get back to work—forcing Canada’s flagship carrier to halt service “until further notice.”