Last year, for the first time in a decade, Denver-based Frontier Airlines turned a profit. It’s on track to do the same this year.

Like many airlines, Frontier charges for luggage in some situations, but it recently stood out from the rest when it announced a charge of up to $100 for a single carry-on bag. Booking a ticket on Frontier’s website rather than through a third-party can reduce the charge to zero. The fee, which made headlines and shocked many, seemed like a public-relations blunder. But Frontier’s management is standing behind it.

“A lot of people try to bring an extra bag on — or too large a bag, and that’s why we have the overhead bin space problem,” says David Siegel, President and CEO of Frontier Airlines. “We are just trying to rebalance things, protect our best customers.”

Siegel says many fliers are not used to an a la carte payment structure, which is why fees may seem unreasonable.

“It will take some time for consumers to learn what the new practices are,” says Siegel. “What we do is let you decide what you want and don’t want, so you only pay for what you use, and otherwise you save the money.”

Whether you think fees are fair or not, it seems like they are here to stay.

“We could do a lot of things for free, but we want to stay in business,” Siegel says.