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.

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.”