Striking Air Canada flight attendants vowed Monday to defy another back-to-work order from Canada's labor tribunal, extending a work stoppage that has cancelled travel for half a million people worldwide.

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.”

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