Spirit Airlines calls off a Thursday reckoning on Frontier’s bid.

On the eve of a planned shareholder meeting on an acquisition by Frontier Airlines, Spirit Airlines said it was putting off the vote and would continue to talk to both Frontier and a rival suitor.

It was a stunning turn in the battle that could change the airline industry. It is a blow to the leaders of Frontier and Spirit, budget carriers that want to combine so they can compete with the nation's four dominant airlines.

The stock-and-cash proposal from Frontier values Spirit at approximately $2.4 billion, while the all-cash offer from JetBlue is worth about $3.6 billion. $350 million is the amount of money the rivals would pay to shareholders if the deal is blocked.

Both marriage proposals are attractive according to a senior vice president and airline industry analyst. They want to know how much they can get.

Frontier did not respond to the request for comment.

The shareholder vote on the transaction was pushed off for the second time. Mr. Hayes said that it was clear that the board had an obligation to reach an agreement with the airline.

The share portion of Frontier's offer allows investors to benefit should the company's share price go up. It attacked the bid as less likely to be approved by regulators. Both bids are likely to be looked at.

The Biden administration has taken a cautious view of large corporate mergers. Over the past two decades, the number of big airlines has plummeted as carriers have merged, and customers are upset with airlines as they deal with mass flight cancellation.

In after-hours trading on Wednesday, shares of Spirit were up 2.2 percent, to $22.90, but still well below the $33.50 offered by the airline.

In February, there was a proposal to combine the two companies. JetBlue responded with an offer. There were rounds of one upmanship and bitter words. JetBlue took aim at Spirit's board, arguing that its ties with Frontier made it hard for it to evaluate the deal.

Barry Biffle was the chief executive of Frontier from 2005 to the present day. The private equity firm once owned both companies. If the deal is approved, he is expected to be the board's leader. Indigo still owns majority of Frontier.

The recommendation to vote in favor of Frontier's bid was reversed last week by the influential advisory firm Institutional Shareholder Services. Another sweetened offer was put forward by the airline.

Frontier and Spirit would become the fifth largest airline in the US, with an 8.2 percent share of the market.

"If our shareholders don't approve the Frontier deal, we're back to a stand-alone," Ted Christie said in an interview with the New York Times. There are issues that we have with the transaction.

The antitrust scrutiny that JetBlue has received from the Justice Department makes it hard for it to get regulatory approval. According to the lawsuit, American would use the partnership toopt a uniquely disruptive competitor. They deny that their deal is anticompetitive.

Frontier and Spirit contend that with cost savings and a larger network, their combined carrier would be able to compete for more customers while still offering very low fares.

One argument against a merger is that it would make it harder for them to keep fares low. Some of the pressure would be alleviated with a merger, which could lead to higher fares and fees on certain routes.

Federal regulators would have to approve any acquisition. They might oppose a merger because it would force them to keep fares low.