Spirit Airlines shares plunged Wednesday on a report that the budget carrier is getting ready to file for bankruptcy protection after revived merger talks with Frontier Airlines parent Frontier Group Holdings collapsed.

Spirit Airlines is reportedly planning to file for bankruptcy following the collapse of a proposed merger with Frontier Airlines that sent its stock into rapid decline.

In the clearest sign yet that bankruptcy is on the itinerary, Spirit Airlines warned early Wednesday that it is preparing for a "statutory restructuring" if it successfully renegotiates terms with its bondholders.