Shares of Spirit Airlines Inc. fell 1.2% in premarket trading Friday, after the air carrier said independent proxy advisor Glass, Lewis & Co. recommended that Spirit shareholders vote for the Frontier Group Holdings Inc. buyout deal. Frontier's stock rose 0.7% and JetBlue Airways Corp. shares eased 0.1%. "Glass Lewis shares our Board's view that the Frontier transaction has an easier path to close and provides third party validation that JetBlue may have ulterior motives behind its offer," said Spirit Chief Executive Ted Christie. Spirit's board has unanimously urged shareholders to reject JetBlue's unsolicited rival tender offer. Glass Lewis' recommendation comes after fellow independent proxy advisor Institutional Shareholder Services (ISS) recommended earlier this week that Spirit shareholders reject the Frontier deal.