CHICAGO, May 24 (Reuters) - Hundreds of pilots at Alaska Air Group Inc are submitting their final votes on whether to authorize a strike over "stalled" contract negotiations, underscoring growing labor tensions in the U.S. airline industry.

The Air Line Pilots Association (ALPA), which represents over 3,000 pilots at the Seattle-based carrier, said the strike authorization vote is aimed at moving what it has describes as "stalled" negotiations forward. The ballot opened on May 9 and is due to close on Wednesday May 25.

Pilots at almost all the major carriers are protesting, demanding higher pay and improvements in "fatiguing" schedules in their new contracts. The protests come at a time when the industry is grappling with a staffing shortage after letting go thousands of pilots at the height of the coronavirus pandemic in 2020.

While a sharp rebound in travel demand and higher fares are projected to help major carriers surpass their pre-pandemic revenue this quarter, recruiting issues have made it harder for them to rebuild capacity and run a smooth operation.

On Tuesday afternoon, ALPA President Joe DePete pushed back against the idea that there was a pilot shortage, tweeting: "Airlines were on the brink of economic disaster. We stood up and went full throttle to prepare our industry for the recovery. But some airlines failed to plan and are blaming the supply of pilots."

Alaska and its pilots have been negotiating a new contract since the summer of 2019. But ALPA has said the company has not "meaningfully" addressed its concerns related to job security and schedule flexibility.

COMPLEX PROCESS

The company's pilots have been conducting pickets, asking for a market-based contract, including higher wages and better benefits. The union said Alaska is on track to lose 180 pilots this year to other carriers as its pilot contract remains below the industry.

Even if the union gets the mandate to declare a strike, Alaska pilots cannot walk off the job until the National Mediation Board grants them permission.

The board will have to first determine that both the parties are at an impasse and further bargaining would not be productive.

This complex process makes it rather difficult for airline workers to strike. The last pilot strike at a U.S. passenger carrier was at Spirit Airlines in 2010.

Alaska said it has made the "most generous" offer to bring its pilot contract in line with industry. It played down the risk of a strike.

"We are in active negotiations with our pilot union and remain optimistic we can reach agreement," the airline said in an emailed statement on Monday.

United Airlines, thus far, is the only major carrier that has reached an agreement with its pilots on new contract. (Reporting by Rajesh Kumar Singh; Editing by Aurora Ellis)