Spirit Airlines rejected a $400 million merger proposal from Frontier this week, saying the offer was financially inadequate and came too late. Spirit Airlines declined an opportunity to merge with rival low-cost airline Frontier on Wednesday.

Spirit, which filed for bankruptcy protection last year, says it has rejected the new Frontier overture but would be open to a higher offer.

Budget carrier Frontier Airlines announced on Wednesday that it has made another bid for fellow discount carrier Spirit Airlines, which is in bankruptcy, for an undisclosed sum.

The Denver-based low-cost carrier said its combination with the Dania Beach, Florida-based Spirit would create a stronger low-cost carrier and benefit “from the very significant synergies Frontier expects to achieve by combining the airlines’ operations.”

Discount carrier says a merger would be a better path out of bankruptcy for Spirit, which has rebuffed the latest proposal.

Frontier Airlines is attempting for a second time to merge with the now bankrupt Spirit Airlines, which declared bankruptcy late last year as budget airlines struggle

Frontier Airlines hoped to create a low-cost airline giant, but Spirit isn’t interested—at least, not at this price. Spirit Airlines has rejected a merger offer with Frontier as it prepares to exit bankruptcy.

Spirit Airlines said on Wednesday it has rejected a bid from rival Frontier Group as it was not favorable for the low-cost carrier and expects to exit bankruptcy in the first quarter. Frontier offered Spirit shareholders $400 million in debt and a 19% stake in Frontier earlier this month,