Video footage captured by Jose L. Rodriguez appeared to show passengers expressing anger and frustration at the airport’s Spirit Airlines (SAVE) counter, with several being led away by police officers. Three people were arrested and face charges of inciting a riot, according to the Broward Sheriff’s Office.

Rodriguez wrote on Twitter that a group of people attending a graduation became “very upset” when their flight was cancelled. “[They] started pounding on the counter and screaming out of frustration. Airport security tried to [calm] them down to no avail,” he added.

@nbc @NBCNews Riot breaks out at #FLL over @SpiritAirlines #cancelled flights. People are angry, some arrested. #worstcustomerservice pic.twitter.com/y1VaH7Lb9w

— José L. Rodríguez (@asg749d) May 9, 2017

Spirit’s flight cancellations are a result of ongoing negotiations between Spirit Airlines and the Air Line Pilots Association (ALPA) over pilots’ contracts.

Paul Berry, Spirit’s spokesman, told Fortune in a statement that his team was “shocked and saddened” by the footage of the incident. “This is a result of unlawful labor activity by some Spirit pilots designed to disrupt Spirit operations for our customers, by canceling multiple flights across our network,” he added.

Berry said that the pilots “put their quest for a new contract ahead of getting customers to their destinations,” and ahead of the safety of their colleagues. He confirmed that the airline has “reluctantly” filed a suit against the Air Line Pilots Association (ALPA) “in order to protect Spirit’s customers from further disruption due to an unlawful job action by Spirit pilots.”

According to documentation provided by Spirit, around 300 flights have been cancelled and the travel plans of over 20,000 customers disrupted over the past seven days, costing Spirit approximately $8.5 million in lost revenue and “irreparable harm to its goodwill with its customers.”