JetBlue is going hostile in its bid for Spirit Airlines and asking Spirit shareholders to reject a proposed $2.9 billion acquisition by Frontier Airlines.

JetBlue is going straight to shareholders of the Florida airline in hopes of pushing its board to the negotiating table. Shares of spirit jumped 17% before the opening bell today.

Spirit has rejected JetBlue’s $3.6 billion offer for the Florida budget carrier twice already, saying antitrust regulators are unlikely to approve an offer from the New York City airline because of its alliance with American Airlines in the Northeast. The Justice Department is suing to block that deal.

Shareholders of Spirit are scheduled to vote June 10 on the Frontier bid favored by the Spirit board.

JetBlue said today that Frontier’s offer is high risk and low value. It made its initial buyout bid for Spirit on April 5, offering $33 per share in cash.

JetBlue is offering $30 a share in cash in its tender offer, but would be open to paying its initial offer price of $33 a share if the board at Spirit enters talks and provides data that JetBlue has requested, the company said. JetBlue said the tender price reflected what JetBlue called Spirit’s unwillingness to share necessary information.

“JetBlue offers more value – a significant premium in cash – more certainty, and more benefits for all stakeholders,” JetBlue CEO Robin Hayes wrote in a letter.

Frontier’s bid would let Spirit shareholders keep 48.5% of the combined airline. It would give Spirit shareholders 1.9126 shares of Frontier plus $2.13 in cash for each of their Spirit shares.

JetBlue’s stock fell slightly while shares of Frontier’s climbed more than 3%.