By Leslie Josephs

Copyright cnbc

Spirit has recently cut a dozen destinations while rivals like United, JetBlue Airways and fellow discount carrier Frontier Airlines have added flights to cities Spirit serves.

Kirby has criticized discount airlines for years, saying that the strong growth they relied on to help fuel profits wasn’t sustainable. On Thursday, he also railed against the model of charging low fares and fees for everything else, saying it sometimes surprised customers.

“You can’t have a business model that customers hate. You can’t have a business model predicated on ‘screw the customer,'” Kirby said Thursday.

Kirby also criticized the model at a different aviation event in Washington, D.C., on Wednesday, sparking a battle with Spirit.

“Scott is finally right about something – it is all about customers,” said a post on Spirit’s X account on Wednesday following his initial comments. “Our Guests love low fares, especially our new Spirit First and Premium Economy options. Maybe that’s why United executives can’t stop yapping about us.”