JetBlue Airways and Spirit Airlines announced on Monday the cancellation of their planned $3.8 billion merger agreement, which would have made JetBlue the fifth-largest air carrier in the nation.

The decision comes shortly after U.S. District Judge William G. Young of the District of Massachusetts squashed the deal over concerns of an “oligopoly” in the airline industry. Regulatory approval was required by July 24 in order to make the acquisition official.