Spirit, which filed for bankruptcy protection last year, says it has rejected the new Frontier overture but would be open to a higher offer.

No-frills, budget airlines often lead the industry in customer complaints, according to government data, so if one were to disappear would it be missed by travelers? That is a question U.S. regulators will be asking after Frontier Airlines said Wednesday that it wanted to buy Spirit Airlines,

Frontier says a merger would be a better path out of bankruptcy for Spirit, as budget carriers struggle with high costs and competition.