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.

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.

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,