• The battle between Frontier and JetBlue for discount airline Spirit is the most contentious in recent years.
• Spirit and Frontier in February announced they planned to merge, but JetBlue swooped in with a surprise, all-cash bid in April.
• Spirit postponed a vote on the deal until July 8 from Thursday.

The most heated airline battle in recent years was set to come to a head on Thursday when Spirit Airlines' shareholders were scheduled to vote on a proposed tie-up with fellow discount carrier Frontier Airlines while rival suitor JetBlue Airways circles with increasingly sweetened takeover bids.

But with hours to go, Spirit delayed the vote until July 8, extending the most heated battle for a U.S. airline in years that could further drive up the price for the budget airline.

Spirit has repeatedly rebuffed sweetened, all-cash bids from JetBlue, arguing that such a takeover wouldn't pass muster with regulators, and has stuck with its plan to combine in an also-sweetened cash-and-stock deal to combine with Frontier, first announced in February.

JetBlue's surprise all-cash bid in April set off a fight over Spirit that last month turned hostile.

If Spirit shareholders end up voting in favor of the tie-up with Frontier, it would put the carriers on the path to creating a budget airline behemoth. The two carriers share a similar business model based on low fares and fees for almost everything else from seat selection to carry-on bags.

If shareholders vote against the deal it opens the door for a takeover by JetBlue, which would retrofit Spirit's yellow planes to look like JetBlue's, including cabins with seatback screens and more legroom.

"JetBlue does not have many options to achieve a step-change in growth, and that explains why JetBlue has pursued this deal so doggedly," said Samuel Engel, aviation consultant at ICF.

JetBlue and Frontier have each argued their proposed transactions are key to their future growth, helping them better compete with large U.S. carriers and get fast access to Airbus narrow-body planes and pilots.

Either deal would create the fifth-largest U.S. airline.

Late Monday, JetBlue said it would raise the reverse breakup fee if regulators don't approve a JetBlue takeover of Spirit to $400 million from $350 million. It also raised the amount it would pay up in advance to $2.50 a share, from $1.50 and added a 10 cent-a-share monthly payment to shareholders starting next year until the deal is consummated or terminated.

JetBlue previously offered to divest some assets in crowded markets to calm antitrust fears, but hasn't said it would give up its alliance with American Airlines in the Northeast U.S., which Spirit has called out as a sticking point in that deal.

JetBlue's latest offer came after Frontier late Friday raised the cash portion of its offer by $2 per share to $4.13 and increased the reverse breakup fee to $350 million to match JetBlue's then-offer.

Spirit has stuck with the Frontier deal. CEO Ted Christie on Tuesday called the Frontier offer "very compelling" and told CNBC the airline wants to "focus our efforts on convincing the shareholders it's the right thing to do."

Proxy advisory firm Institutional Shareholder Services on Tuesday said that "the enhancements by JetBlue may be enough to offset the potential upside of the proposed merger with Frontier" but said it didn't want to change its recommendation in favor of the deal with so little time before the vote.

Spirit previously postponed the vote from June 10 to continue deal talks with Frontier and JetBlue.

War of words

For weeks, JetBlue has argued that Spirit's board hasn't negotiated in good faith or fully considered its offer. It has repeatedly urged the budget airline's shareholders to vote against the Frontier deal.

"The Spirit Board consistently ignored or refused to engage with JetBlue until faced with certain defeat on the original shareholder meeting date and then, in an attempt to avoid the widespread perception of its poor corporate governance, pretended to engage with JetBlue," JetBlue said in a letter Wednesday again urging Spirit shareholders to vote against the Frontier deal.

Spirit has repeatedly denied claims that it hasn't engaged with JetBlue in good faith.

"Our board believes [the Frontier merger] is the most financially and strategically compelling path forward for Spirit with a greater likelihood of closing," Christie said in a video message addressing shareholders on Wednesday.

All three carriers have traded heated words as they try to win over Spirit shareholders before the shareholder vote.

JetBlue late Monday wrote a letter to Spirit shareholders detailing its latest sweetened bid and accusing Spirit of making "misleading statements" regarding its antitrust doubts.

Frontier fired back in a lengthy news release Tuesday saying that "a Spirit acquisition by JetBlue would lead to a dead end — a fact that no amount of money, bluster, or misdirection will change."

The high drama is coming from an already-consolidated industry that hasn't seen a major airline deal since 2016, when JetBlue lost out to Alaska Airlines for Virgin America.

"This is as much as a potboiler for the summer than any trashy novel," said Henry Harteveldt, a former airline manager and president of of Atmosphere Research Group.

High regulatory bar

Either combination of airlines would face high regulatory scrutiny from the Justice Department, after President Joe Biden has made ensuring competition a priority.

"Our duty is to litigate, not settle, unless a remedy fully prevents or restrains the violation. It is no secret that many settlements fail to preserve competition," Assistant Attorney General Jonathan Kanter said in prepared remarks for a speech in Chicago April.

The Justice Department last year sued to undo JetBlue's partnership with American. A trial date has been set for late September.

Frontier has argued that its Spirit deal has a higher chance of passing muster, especially as concerns build over high inflation. Both Frontier and JetBlue say their proposed deals would mean lower fares for consumers.

"In a world where everybody is worried about inflation and the American family, and the American consumer is getting pinched in everything they buy, giving them the option of lower prices is something that I think consumers are going to want," Frontier CEO Barry Biffle said in an interview. "Ultimately, we believe regulators will see it the same way at some point."