Canada's largest airline will begin suspending flights on Thursday after the union representing its flight attendants issued a 72-hour strike notice.

Air Canada will be gradually suspending flights over that period, the carrier said, warning that passengers without confirmed flights should not go to the airport.

The Canadian Union of Public Employees (CUPE), which represents 10,000 Air Canada flight attendants, provided a strike notice early on Wednesday after reaching an impasse in contract talks.

The union said that it has bargained in good faith but Air Canada "refused to address" core issues, such as proposals on wages, and unpaid work.

The airline responded by issuing a 72-hour lockout notice and said on Tuesday night that it had received a union counteroffer seeking "exorbitant increases" and that CUPE had rejected an offer to enter binding, third-party arbitration.

The strike is set to begin at about 01:00 EST (05:00 GMT) on Saturday.

The airline - which operates in 64 countries with a fleet of 259 aircraft - said the unplanned shutdown is "a major risk" to the company and its employees. The flight disruption could affect 130,000 daily customers, including 25,000 Canadians, amid the peak summer travel period.

"By optimally positioning aircraft and crews ahead of a possible stoppage, Air Canada will be able to provide required routine maintenance and more quickly restore regular service," the Montreal-based company said on Wednesday in response to the strike notice.

The first Air Canada and Air Canada Rouge flights will be cancelled on Thursday, with additional flights on Friday also expected to be grounded.

A "complete cessation of flying" will begin on Saturday, the airline said. Air Canada Express flights, which carry about 20% of Air Canada's daily customers, will not be affected.

Customers whose flights are cancelled will be notified and will receive a full refund, the airline said. The company has also made arrangements with other Canadian and foreign carriers to provide customers with alternative travel options.

Customers will be notified of alternative options, but they could take time or might not be immediately possible.

Toronto's Pearson International Airport - Canada's largest airport - said on Wednesday on X that it is closely monitoring the situation, and advised travellers to check directly with Air Canada for flight information. Other airports, including Vancouver International Airport, are also working on contingency plans.

In contract negotiations, the carrier said it offered flight attendants a 38% increase in total compensation over four years, with a 25% raise in the first year. CUPE said the offer is "below inflation, below market value, below minimum wage" and would still leave flight attendants unpaid for some hours of work, including boarding and waiting at airports ahead of flights.

The union asserted that it has bargained in good faith with the airline for more than eight months but Air Canada instead sought government-directed arbitration.

"When we stood strong together, Air Canada didn't come to the table in good faith," CUPE said in a statement to its members. "Instead, they called on the federal government to step in and take those rights away."

Earlier this month, 99.7% of employees represented by the union voted for a strike.