A Spirit Airlines Airbuys A320-200 airplane sits at a gate at the O'Hare Airport in Chicago, Illinois, U.S. October 2, 2014.
A Spirit Airlines Airbuys A320-200 airplane sits at a gate at the O'Hare Airport in Chicago, Illinois, U.S. October 2, 2014. Reuters / Jim Young

Spirit Airlines Inc will go ahead with a vote on its sale to Frontier Group Holdings Inc on Wednesday, with its shareholders expected to shoot it down, according to people familiar with the matter.

Frontier had declined to further raise its sweetened $2.7 billion bid, saying that Spirit should consider last month's revised merger agreement as its "last, best and final offer." JetBlue submitted a sweetened offer worth $3.7 billion this month.

Once the shareholder vote fails, Spirit would be forced to call off the deal with Frontier.

Spirit had previously pushed back the vote four times, hoping it could muster support for the Frontier deal. It will now continue discussions to sell itself to JetBlue Airways Corp, the sources said. The negotiations are progressing favorably, the sources added.

The sources, speaking on condition of anonymity, said that it remains possible that Frontier comes back with a new offer for Spirit.

Spirit, JetBlue and Frontier did not immediately respond to requests for comment.

The latest development represents a setback for Frontier and its chairman Bill Franke, who was instrumental in kicking off the talks between the two sides last year. Franke's airline-focused buyout firm Indigo Partners is a major shareholder in Frontier.

If talks with JetBlue continue to progress favorably, a deal could be announced in the coming weeks, the sources said.

So far, Spirit has rebuffed JetBlue, citing regulatory concerns over the company's Northeast Alliance (NEA) partnership with American Airlines, which is already in the crosshairs of the Justice Department. JetBlue so far has refused to pull out of the NEA and instead offered other sweeteners like a higher break-up fee and route divestments.

Spirit could eventually choose not to do a deal with JetBlue and stay independent, the sources added.

Influential proxy advisory firm Institutional Shareholder Services (ISS) this month recommended that Spirit shareholders vote against the proposed deal with Frontier and said JetBlue's sweetened offer was "more favorable" for shareholders.