The drawn-out bidding war between JetBlue Airways and Frontier Airlines over Spirit Airlines has taken another turn.

JetBlue came in with what it characterized as its “last, best, and final” offer for the airline, at $3.7 billion in cash. Frontier asked Spirit to delay a stockholder vote again on Frontier’s offer of $2.6 billion in cash and stock, which was scheduled to run July 15-27, so it could try to improve its offer for the discount carrier.