Spirit Airlines shareholders are scheduled to vote June 10 on a $2.9 billion buyout offer from Frontier Airlines.

       Shareholders will be voting, in effect, whether to take Frontier’s bid and reject a higher offer from JetBlue Airways.

       The special meeting was detailed in a regulatory filings by Spirit and Frontier. JetBlue did not immediately comment on Wednesday.

       Spirit’s board supports the Frontier deal because of uncertainty about JetBlue’s ability to win approval of its $3.6 billion offer from antitrust regulators.

       Spirit shareholders would get more cash from the JetBlue offer. However, Frontier's proposal would give Spirit shareholders 48.5% of shares in a combined airline, meaning they could come out ahead if the new company's stock rises in value.

       Both Frontier and JetBlue say that acquiring Spirit would help them compete against the nation’s four dominant airlines.

       JetBlue would eliminate Spirit as a so-called ultra-low-cost airline, while Frontier would not. Also, the U.S. Justice Department and several states are already suing to block a JetBlue regional partnership with American Airlines on grounds that it reduces competition.