JetBlue Airways on Monday increased its offer to buy Spirit Airlines, raising the stakes again in a battle over the nation�s biggest budget airline.

New York-based JetBlue said it increased its cash offer to $33.50 per share, or more than $3.6 billion. That is an increase per share of $2 over a June 6 offer and 50 cents over JetBlue�s original April bid.

Frontier Airlines put Spirit in play in February when boards of the two airlines agreed to a merger in which Spirit shareholders would get cash and 48.5% of the combined company. That deal was originally valued around $2.9 billion but has lost value because of a decline in Frontier�s stock price.

Shareholders of Miramar, Florida-based Spirit are scheduled to vote June 30 on the Frontier bid, and JetBlue is trying to convince investors to scuttle the agreement and drive Spirit into JetBlue�s arms.

Spirit said it was reviewing JetBlue�s latest offer. Denver-based Frontier declined to comment. Spirit said last week that its board would give shareholders an update before the June 30 vote.

Spirit�s board has opposed a deal with JetBlue, saying antitrust regulators would never allow it. JetBlue said Monday that it strengthened its commitment to divestitures needed to satisfy regulators but won�t drop a controversial partnership with American Airlines in the northeast U.S.

(AP)