JetBlue's move on Monday came after Spirit had rejected a previous offer from the carrier.
On Thursday, Spirit urged stockholders to reject JetBlue's hostile takeover attempt and accused the carrier of trying to disrupt the merger with Frontier.
"Our view is that the proposed combination of JetBlue and Spirit lacks any realistic likelihood of obtaining regulatory approval," Spirit Airlines board Chairman Mac Gardner said in a statement, noting that Spirit faces a "long and bleak limbo period as we await resolution.
JetBlue first made an offer to acquire Spirit in early April. On Monday, the carrier maneuvered for a hostile takeover by appealing directly to Spirit stockholders. File Photo by Todd Bomser/UPI
"Spirit believes JetBlue's proposals and offer are a cynical attempt to disrupt Spirit's merger with Frontier, which JetBlue views as a competitive threat."
Spirit's main reason behind rejecting previous JetBlue offers is that the Justice Department is already blocking JetBlue's alliance with American Airlines on antitrust grounds.
Shareholders for Florida-based Spirit are scheduled to formally vote on the planned merger with Frontier next month.
"Our pending merger with Frontier is advancing as planned," Gardner added. "And we continue to recommend that Spirit stockholders vote FOR the merger with Frontier on June 10th."
Spirit said in its statement on Thursday that JetBlue has a "host of issues to resolve" and that the carrier's stock price falls "whenever JetBlue makes public comments regarding a proposed transaction with Spirit."
A takeover is considered hostile when one company tries to acquire another that is unwilling to be sold. One way to do this is to lobby a target company's shareholders.