Shares of low-cost carrier JetBlue Airways surged 15% in premarket trading Tuesday after activist investor Carl Icahn disclosed an about 10% stake in the airline.

The shares were undervalued and represented an attractive opportunity, according to a regulatory filing by Icahn on Monday.

Icahn intends to assess the possibility of a board representation at a time when the airline faces the fallout of its $3.8 billion merger with ultra-low-cost carrier Spirit Airlines being blocked by a U.S. judge last month.

Both airlines have asked for an expedited appeal to the ruling and a U.S. appeal court will hear arguments in June.

"We are always open to constructive dialog with our investors...," JetBlue said Tuesday.

Last month, the airline said it was evaluating deeper cost cuts after it forecast higher expenses and a fall in revenue in the current quarter as it grapples with uneven travel demand.

JetBlue's stock has gained 24% since the merger ruling.