TORONTO (AP) — Canada's second largest airline, WestJet, said it canceled at least 235 flights affecting 33,000 passengers Saturday after the maintenance workers union announced it went on strike.

The Aircraft Mechanics Fraternal Association said its members started to strike Friday evening because the airline’s “unwillingness to negotiate with the union” made it inevitable.

The strike came after the federal government issued a ministerial order for binding arbitration on Thursday. That followed two weeks of turbulent discussions with the union on a new deal.

WestJet executives told a news conference in Calgary that another 150 flights could be canceled by the end of the day if there was no resolution to the walkout.

The airline’s CEO, Alexis von Hoensbroech, put the blame for the situation squarely on what he said was a “rogue union from the U.S.” that was trying to make inroads in Canada.

Von Hoensbroech said as far as the airline was concerned bargaining with the union had come to an end once the government directed the dispute to binding arbitration.

“This makes a strike totally absurd because the reason you actually do a strike is because you need to exercise pressure on the bargaining table,” he said. “If there is no bargaining table it makes no sense, there shouldn’t be a strike.”

He added the union had rejected a contract offer that would have made the airline’s mechanics the “best paid in the country."

The surprise strike affecting international and domestic flights is happening during the Canada Day long weekend.

In an update to its membership, the union negotiating committee referenced an order by the Canada Industrial Relations Board that does not explicitly bar any strikes or lockouts as the tribunal undertakes arbitration.

Sean McVeigh, a WestJet aircraft maintenance engineer picketing at Toronto Pearson International Airport Terminal 3 on Saturday, said the strike is an attempt to force the airline to return to a “respectful negotiation.”

McVeigh said the union regrets any inconvenience caused to passengers.

“However, the reason they (passengers) have possibly missed a flight or had to cancel is due to the reason that WestJet is not respectfully sitting down at the table and negotiating,” he said alongside roughly 20 others on the picket line. “We take on a lot of responsibility and we would just like to be appreciated financially,” he said.

At Pearson, WestJet passengers Samin Sahan and Samee Jan said they had been planning to leave Saturday with extended family members on a trip to Calgary that had been planned for six to eight months.

Sahan said they had received emails earlier in the day telling them their flight had been rescheduled for Monday, but they went to the terminal anyway. He said their efforts to seek clarification combined with the strike had left their travel plans up in the air.

“This inaction is hurting a lot of people, they’re own company as well as their customers who will likely no longer be their customers ever again,” Sahan said.

Jan called the situation “sad.”