Hawaiian shares were trading at $13.40 in morning trade, below Alaska's offer price of $18 per share made public on Sunday, with some analysts saying regulatory approval was far from certain.
The company's shares had taken a beating in recent months due to the impact of the Maui wildfires, high fuel costs and jet engine recall issues at some of its Airbus planes. Its shares have fallen 52.6% so far this year.
Hawaiian presently has a negative price-to-earnings (PE) ratio of 1.5, reflecting losses, compared to a positive forward 12 months PE ratio of 8.2 for Alaska Air, according to LSEG.
Alaska and Hawaiian said on Sunday the deal, valued at $929.4 million (€858 million) on an equity basis, will expand their networks and offer more choices to passengers.
'Good Common Sense'
"This transaction makes good common sense for both airlines," TD Cowen analyst Helane Becker wrote in a note.
The deal will enable Alaska to grow in the lucrative Asia Pacific market, while Hawaiian customers can travel non-stop to the US mainland, Becker added.
"The high premium of the deal is justified by the extensive network synergies the combined entity would be able to achieve, with minimal further investment," said Craig Jenks, president of New York-based aviation consultancy Airline/Aircraft Projects, in reference to the 270% premium.
However, regulatory resistance to the merger is a possibility. Under a hawkish Biden administration, the US Justice Department had filed a lawsuit in March to stop JetBlue from buying Spirit Airlines, saying the planned merger 'would put travel out of reach for many cost-conscious travelers.'
JetBlue shares pared losses from premarket to trade flat, while Spirit shares were up 6.5% on Monday.
Shares of Seattle-based Alaska Air were down 17.6%.