Shares in JetBlue rose more than 15 per cent before the US market opened on Tuesday as activist investor Carl Icahn took an almost 10% stake in the airline.

The businessman, who purchased the shares in January and February, said in a regulatory filing that he believes JetBlue’s stock is undervalued and represents an attractive investment opportunity.

The stock has fallen about 29 per cent in the past year.

Mr Icahn has had talks and plans to continue talking with JetBlue with regard to possible representation on its board of directors.

JetBlue did not immediately respond to a request for a comment.

JetBlue was dealt a major blow last month when a federal judge sided with the Biden administration and blocked JetBlue Airways from buying Spirit Airlines, saying the $3.8 billion deal would reduce competition.

Both airlines have filed their intention to appeal to a higher court, and a June hearing date has been set.

New York-based JetBlue had argued it needed the deal to grow quickly and better compete against bigger rivals that dominate the US air-travel market. But shortly after the ruling JetBlue told Spirit it may terminate the agreement.

JetBlue, the nation’s sixth-largest airline by revenue, must now come up with another growth plan.

That job will fall to chief executive Joanna Geraghty, successor to Robin Hayes, who engineered the deal.

JetBlue has struggled to recover from the Covid-19 pandemic while its bigger rivals have returned to healthy profitability.

JetBlue has lost more than $2 billion since the start of 2020.