The US Department of Justice has filed a lawsuit to block JetBlue’s planned acquisition of Spirit Airlines in a bid to prevent the airline sector from becoming too concentrated. The department has argued that the $3.8 billion merger would result in less competition and higher fares for customers. It claims that the deal would combine JetBlue’s strength in the Northeast and Florida with Spirit’s foothold in the south, leading to a monopoly on multiple routes. The lawsuit comes as transportation officials are also monitoring the deal closely. JetBlue’s proposed acquisition of Spirit Airlines was first announced in December last year.