(Bloomberg) -- American Airlines Group Inc. and its pilots union are close to reaching an agreement on a new contract after weeks of focused negotiations. 

The two sides could have a tentative agreement by the end of this month, said a person familiar with the talks who asked not to be named discussing a private matter. Negotiations will continue even as aviators with the Allied Pilots Association overwhelmingly voted to support a strike Monday. 

Three of the nation’s four largest airlines are in contract talks with pilots, who are seeking major improvements after the pandemic suspended negotiations and as carriers rake in record revenue. Spending for labor and fuel are the largest expenses for carriers, and pilots are the highest-paid group among airline employees. 

About 99% of American’s pilots voting approved the strike authorization ballot, the pilots union said in a statement, though they can’t walk off the job as a result of the vote. Members picketed outside the airline’s 10 major hubs on Monday, alongside digital billboards that read “American Airlines Pilots Ready to Strike!” 

The APA represents 15,000 pilots at American Airlines.

A strike is typically a last resort in labor disputes, and is particularly elusive among US airline workers. The Railway Labor Act, which governs the industry’s negotiations, has a lengthy process that includes a required strike authorization vote followed by additional, time-consuming steps with the union and company. A strike must then be allowed by the National Mediation Board. The last pilot strike under the law was at Spirit Airlines Inc. in 2010. 

“Our pilots’ resolve is unmistakable,” APA President Ed Sicher said in a statement. “We will not be deterred from our goal of an industry-leading contract.”

In an update to members on April 24, pilot union negotiators said “a handful of open items remain” in the contract talks and “we look forward to informing you of additional bargaining successes.” 

A strike authorization vote allows pilots to express their desire to get a deal done, “and we respect the message of voting results,” American said in a statement. The carrier said it’s confident an agreement “is within reach and can be finalized quickly.” 

Southwest Airlines Co. and United Airlines Holdings Inc. remain in contract talks, while Delta Air Lines Inc. pilots in March approved a new contract providing at least 34% in cumulative pay hikes over four years. Southwest aviators, represented by the Southwest Airlines Pilots Association, began a strike authorization vote Monday, the union said. The airline called it a “contract negotiating tactic.”

Read more: Delta Pilots Approve Contract Seen Setting Industry Standard

Delta’s contract is the richest ever negotiated by a mainline US carrier, with $7.2 billion in improved pay, benefits and quality-of-life improvements over its term. American Airlines’ pending contract would represent an increased $8 billion in spending over its term, Chief Executive Robert Isom has said.

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