The Department of Justice filed a lawsuit Tuesday to block JetBlue’s purchase of ultra-low cost Spirit Airlines in hopes of countering the merger in an industry already rife with consolidation, Politico reports. The merger, if successful, would form the country's fifth-largest airline. Both airline companies have conceded that the merger would lead to fewer seats for customers, but maintain that fares would stay low, according to Politico. The $3.8 billion acquisition was first proposed in July following Spirit's failed merger with Frontier Airlines. State attorneys general from the District of Columbia, Massachusetts and New York have also joined the suit.