Pilots at American Airlines voted to authorize a strike, a move that is highly unlikely to lead to an immediate walkout but puts more pressure on the airline to reach a new contract with the pilots’ union.

The Allied Pilots Association said Monday that more than 96% of its 15,000 members voted, and among those who did, 99% favored authorizing the union to call for a strike.

Federal law prohibits airline unions from striking without the tacit approval of a U.S. mediation board – a rare step that has not occurred in this case. Congress and the president can also act to prevent a strike if one appears imminent.

Airline unions like to take strike votes, however, which they believe increase their leverage at the bargaining table.

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.

American pilots planned to picket later Monday at airports around the country.