Air Canada has delayed its planned limited flight resumption after the flight attendants’ union defied a federal order to return to work.

The Canadian Industrial Relations Board had directed staff to resume duties Sunday following binding arbitration imposed by Jobs Minister Patty Hajdu.

CUPE, representing the attendants, called the order “blatantly unconstitutional” and said members remain on strike, demanding fair contracts and pay.

The walkout, which began Saturday over pay and scheduling, has already grounded about 700 flights daily, affecting roughly 100,000 travelers, NBC News has reported.

Air Canada now expects to restart operations Monday evening and is offering refunds or rebooking options.