The Montreal-based airline said labor negotiations with its 10,000 flight attendants are at an impasse and warned that the carrier may begin to shut down operations as early as Saturday without an agreement.

Air Canada, Canada’s largest airline, says labor negotiations are “at an impasse” after making a sweetened offer to the union representing its 10,000 flight attendants.

A cabin crew strike threatens to shut down Air Canada for 72 hours from Saturday. Canada’s largest airline admitted it had reached an “impasse” in talks with a union representing 10,000 flight attendants.