WestJet cancelled nearly 700 flights as of Sunday, upending plans for close to 100,000 passengers as an unexpected strike by plane mechanics entered its third day on the busiest travel weekend of the season.

Some 680 workers, whose daily inspections and repairs are essential to airline operations, walked off the job on Friday evening despite a directive for binding arbitration from the federal labour minister.

Since Thursday, tracking service FlightAware shows WestJet has cancelled 687 flights scheduled to fly between then and the end of the Canada Day long weekend.

As of Sunday morning, 77 per cent of the day's trips had been called off, with WestJet topping the global list for cancellations among major airlines Saturday and Sunday.

Trevor Temple-Murray was one of thousands of customers scrambling to rebook after their trips were scrapped less than a day in advance.

"We’ll just have to wait it out," said the resident of Lethbridge, Alta., who was on hold in the parking lot of the Victoria airport trying to get a plane to Calgary, his wife and two-year-old son beside him in the car.

Their 6:05 p.m. flight had been cancelled, and they wouldn't know until the evening whether a scheduled 7 a.m. flight the next day would go ahead.

“There are a lot of angry people in there," Temple-Murray said, pointing at the airport.

Other travellers took to social media to express their frustration — sometimes in colourful language.

One customer said the airline informed them only at 11:12 p.m. on Saturday that their next-day flight out of Las Vegas was cancelled, calling the last-minute move "scumbag behaviour."

Both WestJet and the Airplane Mechanics Fraternal Association have accused the other side of refusing to negotiate in good faith.

WestJet Airlines president Diederik Pen has stressed what he calls the "continued reckless actions" of a union making "blatant efforts" to disrupt Canadians' travel plans, while the association claimed the Calgary-based company has refused to respond to its latest counterproposal. In an update to members Sunday, it said mechanics were "the victim of WestJet’s virulent PR campaign that you are scofflaws," citing "calumnies" against workers around their right to strike.

Not everyone was vexed by the weekend's labour turbulence.

"We are seeing a huge surge in bookings, presumably from passengers scrambling to save their long weekends," said Flair Airlines spokeswoman Kim Bowie.

The job action comes after union members voted overwhelmingly to reject a tentative deal from WestJet in mid-June and following two weeks of tense talks between the two parties.

As the clock ticked down toward a Friday strike deadline, the impasse prompted Labour Minister Seamus O'Regan to step in, mandating that the airline and union undertake binding arbitration headed by the country's labour tribunal.

That process typically sidesteps a work stoppage. WestJet certainly thought so, stating the union had "confirmed they will abide by the direction."

"Given this, a strike or lockout will not occur, and the airline will no longer proceed in cancelling flights," the airline said Thursday.

The mechanics took a different view. The union negotiating committee said it would "comply with the minister’s order and directs its members to refrain from any unlawful job action." Less than 24 hours later, workers were on the picket lines.

A decision from the Canada Industrial Relations Board seemed to affirm the legality of their actions regardless of protocols around arbitration, a process that typically averts work stoppages rather than starting them.

"The board finds that the ministerial referral does not have the effect of suspending the right to strike or lockout," the tribunal wrote Friday.

O'Regan said the next day the board's ruling was "clearly inconsistent" with the direction he provided, but later added he respected the body's independence. He met with both sides Saturday evening.

"I told them they needed to work together with the Canada Industrial Relations Board to resolve their differences and get their first agreement done," he said in a social media post.

However, O'Regan has broad authority under the Canada Labour Code. Though his initial directive to the tribunal for binding arbitration may have presumed a strike was off the table due to precedent, the labour minister could take a range of steps to "secure industrial peace and to promote conditions favourable to the settlement of industrial disputes," the legislation states.

"To those ends the minister may ... direct the board to do such things as the minister deems necessary."

Both parties were set to meet Sunday, the union said

"It's uncharted territory. We're breaking a new precedent here," Ian Evershed, a mechanic and union representative involved in the talks, said in a phone interview Sunday.

The union's goal remains a deal hammered out through bargaining rather than arbitration — a route it opposed from the get-go.

“That process could take months to go through," he said, stressing a strike puts pressure on the employer. That stance clashes with WestJet's statement that the job action boiled down to "pure retaliation" given that a deal would be settled via arbitration regardless.

"It was our only move," Evershed said, adding a negotiated deal may yet emerge.

In a submission to the tribunal last week, WestJet lawyers said the union sought "an unreasonable and extortionate outcome" and intentionally manoeuvred to place the strike date at the height of summer travel.

The union says its demands around wages would cost WestJet less than $8 million beyond what the company has offered for the first year of the collective agreement — the first contract between the two sides. It has acknowledged the gains would surpass compensation for industry colleagues across Canada and sit more on par with U.S. counterparts.

WestJet says it has offered a 12.5 per cent wage hike in the first year of the contract, and a compounded wage increase of 23 per cent over the rest of the five-and-a-half-year term.

This report by The Canadian Press was first published June 30, 2024.

— With files from Dirk Meissner in Victoria