Barry Biffle, the CEO of low-cost carrier Frontier, shot back at his United counterpart Wednesday for his comments predicting the end of Spirit Airlines and the budget flight industry as a whole. 

“That’s cute,” Biffle said Wednesday at the travel-centric Skift Global Forum, CNBC reported.“If he’s good at math, he would understand that we have a [flight] oversupply issue in the United States.”

Biffle came to Spirit’s defense after United CEO Scott Kirby said the low-cost airline, which declared bankruptcy for the second time this year, was going to go out of business. When asked at a conference last week why he was so sure, Kirby replied, “Because I’m good at math.”

Biffle’s ambition to have Frontier surpass Spirit as the top ultra-low cost carrier would make him the “last man on a sinking ship,” Kirby added.

In addition, when asked whether low-cost airlines like Frontier survive based on extra capacity left over by larger carriers like United, Biffle didn’t mince words.

“That’s like the CEO of Nordstrom saying ‘I allow customers to buy jeans from Walmart.’”

Biffle claimed Frontier is attracting people who may not have flown otherwise, or who are trying to save on flight costs so they can spend big on other items like luxury hotels. Biffle also bragged about Frontier’s lower costs: 7.50 cents per available seat mile, not counting fuel, compared with a higher 12.36 cents for United. 

United Airlines and Frontier Airlines did not immediately respond to Fortune‘s request for comment.

United CEO’s conflict with low-cost flying

Kirby has lambasted low-cost carriers for years, and last week he again tore into their economic model and the myriad add-on fees for everything from a carry-on bag to priority boarding, saying “you can’t have a business model predicated on ‘screw the customer.’” United, for its part, introduced paid priority board seating for some customers in 2018. 

Low-cost carriers have struggled over the past few years thanks to rising costs, regulatory demands, and a shift in consumer preferences. The competition from larger carriers, many of which have introduced basic fares that compete with low-cost carriers, has also dealt a blow to these airlines. 

Frontier was profitable for the first time in four years in 2024, but reported a net loss for the first six months of this year. The company was in the red to the tune of $70 million in the second quarter, but predicted higher unit revenue growth in the third quarter would lay the foundation for a return to profitability in 2026.