CHICAGO (Reuters) - Shortages of new planes, jet engines and pilots have left U.S. airlines with little choice but to pursue growth through acquisitions - which then puts them in the crosshairs of anti-trust regulators.

Alaska Airlines (ALK.N) surprised analysts and industry officials with its plan to buy Hawaiian Airlines (HA.O) for $1.9 billion even before a judge rules on the U.S. Department of Justice's (DOJ) lawsuit aimed at blocking JetBlue's (JBLU.O) proposed merger with Spirit Airlines (SAVE.N).

But supply and labor constraints are so onerous that airlines like Alaska will likely keep chasing deals despite the Biden administration's aversion to more consolidation. Currently, American Airlines (AAL.O), United, Delta and Southwest Airlines (LUV.N) control 80% of the domestic market, leaving little room for growth.

"This is an industry that is constantly looking for an angle," said Addison Schonland, partner at consulting firm AirInsight. "If Alaska didn't move on Hawaiian, what would stop somebody else moving on Hawaiian?"

The deal will provide Alaska - primarily a domestic carrier that flies narrowbody planes - Hawaiian's widebody jets, pilots and international networks, opening a runway for growth in long-haul international markets.

In an interview, Alaska CEO Ben Minicucci said it was the right time to do the deal, which he described as "a great investment, a great step change" for the company.

Alaska told analysts on Sunday that pursuing long-haul international flying on its own would be much more expensive and much more difficult.