Spirit Airlines said in a regulatory filing Wednesday that it is rejected a merger offer from Frontier Group Holdings' (ULCC) Frontier Airlines and expects to emerge from bankruptcy in Q1.

The company has decided "barring new developments, not to further delay its planned emergence from Chapter 11," Spirit Airlines said.

Frontier said Wednesday it made what it described as a "compelling" proposal for a combination of its Frontier Airlines subsidiary with Spirit Airlines through the issuance of new Frontier debt and stock.

Frontier said the proposed merger "would provide meaningful value to Spirit financial stakeholders, in excess of Spirit's standalone restructuring plan."

According to a Wednesday regulatory filing, Frontier proposes, among other things, to issue $400 million in debt and 19% of common equity at closing to acquire Spirit's assets.

ULCC shares were up 2.8% in recent premarket activity.