JetBlue Raises Offer to Buy Spirit Airlines—Again

JetBlue Airways Corp. isn’t backing down in its fight to buy Spirit Airlines Inc. raising its offer yet again in an effort to outmaneuver rival Frontier Airlines.

JetBlue on Monday proposed a $400 million breakup fee, which it would pay to Spirit if regulators block the merger, up from the $350 million it had previously pledged. JetBlue also said it would prepay $2.50 a share once investors approve the deal, up from $1.50 a share previously.