JetBlue and Spirit Airlines announced a merger, really the acquisition of Spirit by JetBlue, this week. The purchase price is $3.8 billion, with each Spirit shareholder to receive $33.50 per share. If the deal goes through (the U.S. Justice Department can say no) JetBlue will join a new “Big 5” of U.S. airlines.

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Competition may well increase among the new Big Five. But the largest ULCC (ultra-low-cost carrier), Spirit, would vanish, leaving the low-fare domestic market to Frontier, Allegiant, and even smaller carriers.

“Spirit is going to disappear, and with it, its low-cost structure,” William McGee of the American Economic Liberties Project told AP. “There is no question that fares are going to go up.”

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