Spirit Airlines has delayed a vote on its planned tie-up with Frontier Airlines for a fourth time as concerns mount about a lack of shareholder support.

Spirit said Wednesday it now plans to hold the vote, most recently scheduled for Friday, on July 27 so it can continue deal talks with Frontier and with JetBlue Airways, whose competing bid for Spirit has thrown the original deal into question.

Over the weekend, Frontier Airlines’ CEO, Barry Biffle, wrote to his Spirit counterpart to ask for a delay on the vote.

“We still remain very far from obtaining approval from Spirit stockholders,” Biffle said in the letter.

In the event Spirit breaks its deal, first agreed to in February, and finds JetBlue’s offer superior, Spirit would owe Frontier a break-up fee of more than $94 million.

Spirit previously rebuffed JetBlue’s all-cash takeover offers, even in light of repeatedly sweetened terms, in favor of the original Frontier deal. But it most recently said it is negotiating with both airlines, raising doubts about the fate of the tie-up with Frontier.

JetBlue and Frontier didn’t immediately comment Wednesday.

Either combination of airlines would create the fifth-largest U.S. carrier.