In a March letter to President Biden's administration, U.S. Senators Elizabeth Warren and Bernie Sanders, among others, urged the Justice Department to carefully consider whether a $6.6 billion merger between Spirit and Frontier Airlines would be good for consumers. That merger would theoretically have made Frontier the fifth largest domestic carrier. "Even as the fifth-largest carrier, JetBlue, with Spirit, would have only 9% market share, compared to 13% for the fourth-largest airline and 23% for the largest carrier. After the combination and with its committed upfront divestitures, the largest seat share a combined JetBlue-Spirit will have in any of its largest metro areas is 40%, compared to the 57-91% share legacy carriers have in their largest metro areas," JetBlue said in a release. "The four largest carriers control more than 80% of the market.