A federal judge has blocked the proposed $3.8 billion acquisition of Spirit Airlines (SAVE) by JetBlue Airways (JBLU 1.05%), sending both carriers back to the drawing board to pursue growth. JetBlue's options as a stand-alone look rosier than Spirit's, with investors sending Spirit shares down more than 50% while JetBlue stock was in the green Tuesday afternoon.

Competitive concerns resonate in court

JetBlue and Spirit have been a turbulent match from the beginning. In 2022, Spirit had agreed to be acquired by Frontier Group Holdings, but eventually succumbed to an aggressive effort by JetBlue to outbid Frontier and claim the prize for its own.

Frontier warned at the time that a JetBlue/Spirit combination would be hard for regulators to swallow. The two airlines heavily overlap on the U.S. East Coast and Florida and operate very different models, leading to questions about whether JetBlue's purchase of Spirit would eliminate a low-fare leader.

The U.S. Justice Department sued to block the merger, and federal judge William Young, in a ruling Tuesday, sided with the government and ruled that the deal is anticompetitive. Young called the airline industry "an oligopoly that has become more concentrated due to a series of mergers," and said antitrust law was clear.

"The Clayton Act, a 109-year-old statute, requires this result -- a statute that continues to deliver for the American people," Young wrote in his decision.

The economy has shifted a lot since the deal was first announced, and airlines are showing signs of weakening demand. JetBlue shares are up because, arguably, the last thing an airline needs heading into a recession is more capacity and a complex integration. For Spirit, the deal leaves the company vulnerable at an inopportune time.

Are JetBlue and Spirit stocks buys after the judge's decision?

The ruling leaves neither company well positioned for the long term. JetBlue pursued this risky acquisition strategy in part because the airline needed jets and pilots to grow, and wanted to take advantage of opportunities to cross-sell Spirit customers and grow in core Spirit markets. Absent a deal, questions about how JetBlue grows from here are going to be difficult to answer.

Spirit shares, on the other hand, are falling because a lot of the airline's valuation was tied to the price JetBlue was willing to pay for it. Absent a buyer, Spirit faces the unenviable task of surviving a potential recession on its own.

It is possible that Frontier will eventually return with another offer for Spirit, a deal that from the beginning looked more palatable to regulators than JetBlue's proposal. But that deal would also likely face some regulatory pushback, and is unlikely to come together quickly in this environment.

The future of both airlines is a lot less clear today than it was only yesterday, and investors would be wise to allow time for the dust to settle before jumping on board either stock.