Frontier Airlines on Friday added more cash and a larger breakup fee to its offer to buy Spirit Airlines, and the Spirit board repeated its preference for Frontier over a rival bid by JetBlue Airways.

Frontier added $2 in cash to its previous offer of $2.13 in cash and 1.9126 shares of Frontier for each Spirit share.

The Denver-based airline also raised to $350 million the amount it would pay Miramar, Florida-based Spirit if antitrust regulators stop the deal, matching JetBlue’s proposed breakup fee.

Spirit said that, given the sweetened terms, its board reiterated its unanimous recommendation that shareholders approve the Frontier offer at a special meeting next Thursday.

Frontier’s move was the latest gambit in a fight between Frontier and JetBlue to see who gets the nation’s largest discount airline. On Monday, New York-based JetBlue raised its all-cash offer to $33.50 per share, or more than $3.6 billion.