The $3.8 billion deal has been approved by shareholders, but the US Justice Department has now said it has the potential to drive up airfares in the budget market.

A lawsuit has been filed in Boston arguing the merger would lead to higher prices for Spirit’s customers, who rely on its ultra low-cost formula. JetBlue proposes axing the Spirit brand and operating model in favour of its hybrid approach if the deal is approved.

Associated Press quoted the lawsuit as saying Spirit provided about half of all ultra-low-cost airline seats in the industry, adding its elimination would “leave tens of millions of travellers to face higher fares and fewer options”.

JetBlue argues it and Spirit “only overlap on 11% or less” of the non-stop routes on which both fly. JetBlue claims combining with Spirit will allow it to challenge the “big four” carriers – American Airlines, Delta, United and Southwest – which account for 80% of the US market.

Separately, JetBlue has confirmed the launch of its first services to continental Europe. A daily Paris Charles de Gaulle-New York JFK service will commence on 29 June. It follows the success of the carrier’s debut transatlantic flights from JFK and Boston to Heathrow and Gatwick, which began in August 2021.