Pilots at American Airlines have voted to authorise a strike over contracts.
The Allied Pilots Association said on Monday that more than 96% of its 15,000 members voted, and among those who did, 99% favoured authorising the union to call for a strike.
Although a walkout is highly unlikely due to federal laws prohibiting airline unions from striking without the approval of a US meditation board, it puts more pressure on the airline to reach a new contract with the pilots' union.
Congress and the president can also act to prevent a strike if one appears imminent.
Airline unions like to take strike votes which they believe increases their leverage at the bargaining tables.
A spokeswoman for the airline said American is confident that it can reach an agreement with the union quickly.
"We understand that a strike-authorization vote is one of the important ways pilots express their desire to get a deal done, and we respect the message of voting results," said the spokeswoman, Sarah Jantz.
American and United Airlines are under pressure to match or beat terms that rival Delta Air Lines accepted with its pilots, who earlier this year won 34% raises over a four-year contract.
The American pilots' union said it is also seeking scheduling changes that union officials say will improve efficiency and prevent the kind of widespread delays and cancellations seen last summer.
"The summer travel season is almost here, and we're all wondering whether this will be another summer of uncertainty for American Airlines," union President Ed Sicher said.
Mr Sicher also revealed pilots will be prepared to strike if necessary.
He added: "We will strike if necessary to secure the industry-leading contract that our pilots have earned and deserve – a contract that will position American Airlines for success.
"Our pilots’ resolve is unmistakable. We will not be deterred from our goal of an industry-leading contract.”
However, American Airlines spokesperson Curtis Blessing said in a statement he believes an agreement with the pilots is within reach.
A strike would only happen if the union’s negotiations with American Airlines’ management, which are currently ongoing, break down.
The National Mediation Board would also get involve in a bid to get the discussions back on track.
Mr Blessing said: “We remain confident that an agreement for our pilots is within reach and can be finalised quickly."
American pilots planned to picket later Monday at airports around the country.
