Discovery Capital Management has called on Spirit Airlines to abandon its deal with Frontier Airlines in favor of a higher cash bid by JetBlue Airways, putting additional pressure on the budget carrier to walk away from the current arrangement.

Spirit has postponed a shareholder vote on the deal multiple times, saying it needs more time to engage with shareholders who are not supportive of the Frontier deal. Most recently, Spirit on Wednesday said the vote would take place on July 27, rather than July 15 as previously planned. Frontier’s CEO over the weekend argued a new delay was needed, saying his company was still “very far” from obtaining sufficient backing for the merger.

In a statement Tuesday, 1.4% shareholder Discovery slammed Spirit’s board for refusing to “recognize the superiority of the JetBlue bid” and continuing to recommend shareholders vote for the “economically inferior Frontier merger proposal.” The investor also claimed that 55% of shareholders cannot exercise their voting rights because they bought their shares after the May 6 record date.

Discovery’s letter comes shortly after another shareholder, TIG Advisors, said it would vote against the Frontier transaction, favoring a deal with JetBlue instead.

Jet Blue, meanwhile, issued its own statement Wednesday criticizing the delay in holding the special meeting.

“By moving the Special Meeting again, the Spirit Board is delaying the ability of Spirit shareholders to receive JetBlue’s superior terms,” said Jet Blue chief executive Robin Hayes.

Frontier’s cash and stock offer values Spirit at around $24 per share. JetBlue offered $34.15 per share in cash. Shares in Spirit closed down 1% Tuesday at $24.17.