Air Canada will start cancelling flights on Thursday as the airline prepares for a complete shutdown this weekend.
It faces a potential work stoppage by flight attendants on Saturday.
The airline announced it will gradually suspend operations to ensure an orderly shutdown.
The first cancellations begin on Thursday, followed by more on Friday.
Air Canada and Air Canada Rouge will stop all flights by the weekend.
Air Canada Express flights run by Jazz and PAL Airlines will continue normal operations.
The union representing about 10,000 Air Canada flight attendants issued a 72-hour strike notice today.
The airline responded with a lockout notice.
"We regret the impact a disruption will have on our customers, our stakeholders and the communities we serve," said Air Canada Chief Executive Officer Michael Rousseau.
Passengers whose flights are cancelled will receive notification and qualify for full refunds.
Air Canada has arranged alternative travel options with other Canadian and foreign carriers where possible.
On Tuesday, Air Canada said contract talks had stalled.
The two sides remain far apart in their negotiations.
The union says its main concerns centre on what it calls flight attendants' "poverty wages" and unpaid labour when aircraft are not airborne.
"Despite our best efforts, Air Canada refused to address our core issues,” said the union in an online bargaining update.
The union rejected the airline's proposal for binding arbitration.
It prefers to negotiate a deal that members can vote on.
Unlike negotiated tentative agreements, arbitrator decisions are final without member voting.
The union also said arbitrators "rely on precedent and the status quo to make their determinations," which conflicts with its bargaining objectives.
