CHICAGO (CBS) — Several Spirit Airlines flights to and from Chicago have been cancelled, as the company accuses pilots of an illegal slowdown amid a contract dispute.

At least nine Spirit flights to and from O’Hare International Airport have been canceled as of Tuesday morning. Another four have been delayed. That could be due to “pilot unavailability,” which Spirit said caused 81 cancellations nationwide on Monday.

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Passengers were not pleased.

“We never got an email, no text message that the flight was cancelled, so it’s very frustrating to know at the last minute that your flight is cancelled,” Jude Akpede said. “These are people’s lives, and a lot of people are going for interviews, and stuff like that that they have to be in New York today, and cancelling the flight, it doesn’t look good. We’re very frustrated.”

Travelers clashed with Spirit employees and police at a check-in counter at Fort Lauderdale-Hollywood International Airport after a flight was cancelled at the last minute Monday. Three people were arrested.

A total of nine Spirit flights were cancelled at Fort Lauderdale, causing hundreds of passengers to be stranded.

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Spirit said 20,000 customers have been affected by more than 300 cancelled flights since last week, blaming “pilot unavailability.”

The airline sought a court order seeking a halt to an alleged job action by the pilots’ union, claiming pilots are illegally refusing work “in order to bring pressure on Spirit during current negotiations.” The company claimed it has caused “irreparable harm to Spirit and the traveling public.”

The Air Line Pilots Association has denied Spirit pilots are engaged in any type of job action, and said they are “continuing to do everything possible to help restore the company’s operations.” The union also promised to defend the pilots against the “unwarranted” legal action by the airline.

According to Spirit’s lawsuit, the two sides are “far apart on pay rates” for pilots.

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The airline’s lawsuit also alleges some pilots have turned down “open time” and last-minute assignments due to the dispute, and intimidated others who have accepted such assignments. The union has denied those allegations, and said it encourages pilots to pick up open time when they wish.