The union representing American Airlines’ pilots escalated tensions over contract talks by voting to authorize a strike, even though the carrier said it is close to a deal.

It’s the first in a long list of steps that could lead to pilots walking off the job as the Allied Pilots Association tries to exert pressure on American Airlines ahead of the busy summer travel season. The Southwest Airlines Pilots Association also started voting to authorize a strike Monday, a move that has become a standard step in the contract negotiation process among major airline labor unions.

For American’s pilots, the strike authorization vote began on April 1 and ended April 30, and over 96% of members participated, with 99% of participants voting in favor of authorizing a strike.

“The summer travel season is almost here, and we’re all wondering whether this will be another summer of uncertainty for American Airlines,” said Capt. Ed Sicher, Allied Pilots Association president. “Fortunately, there is an alternative. By embracing the win-win scheduling and work rule improvements APA has presented at the bargaining table, management can take steps to improve the airline’s operational reliability and efficiency.”

A strike authorization vote doesn’t necessarily mean a strike or a work stoppage will happen. The vote garners support from the union’s membership in the event that the union would like to enact a strike.

The strike threat is intended to speed up contract talks that are now in their third year. The Railway Labor Act, which covers the airline industry, doesn’t allow pilots to walk off the job unless federal regulators agree that the two sides are at an impasse – something that would likely be months or years away.

American Airlines spokeswoman Sarah Jantz said the carrier remains confident that an agreement is within reach and can be finalized quickly.

“The finish line is in sight,” Jantz said in an email. “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. Importantly, the results don’t change our commitment or distract us from working expeditiously to complete a deal. We remain focused on completing the handful of matters necessary to reach an agreement our pilots deserve.”

The Allied Pilots Association will be hosting informational pickets at 10 of the airline’s major hubs, including DFW International Airport on Monday.

Sicher said the union “will strike if necessary” to secure a contract for American’s pilots.

“The strike authorization vote is one of several steps APA has taken to prepare for any eventuality and use all legal avenues available to us for contract improvement and resolution,” he said. “The best outcome is for APA and management to agree on an industry-leading contract – achieved through good-faith bargaining – benefiting our pilots, American Airlines, and the passengers we serve.”

American Airlines CEO Robert Isom said pilot pay would be boosted by $8 billion over four years under a contract proposed by the Fort Worth carrier. American’s pilots would receive a 21% pay increase on average in the first year, Isom said in a video to pilots in March.