The Association of Flight Attendants threw its support behind Sen. Ed Markey Edward (Ed) John MarkeyA game theorist's advice to President Trump on filling the Supreme Court seat Watchdog confirms State Dept. canceled award for journalist who criticized Trump 3 reasons why Biden is misreading the politics of court packing MORE (D-Mass.) in the Massachusetts Democratic Senate primary on Saturday, marking one of the first major endorsements in what is expected to be a highly contentious race.

The union's president, Sara Nelson, called the endorsement "personal" in a statement, citing her working relationship with the longtime Massachusetts lawmaker.

"He fights every day like our pain is his pain. He demands results because real people fuel his fight," Nelson said in a statement.

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"No one in Washington fights harder for our security, from screening all checked baggage, keeping knives off planes or closing loopholes on cyber vulnerabilities. Ed fights for the working class and the people who need a champion. That’s who Ed Markey is. He stands with us. And today we stand with him," she added.

Markey is facing a number of primary challengers ahead of the state's Senate primary next year, most notably from fellow Massachusetts progressive Rep. Joe Kennedy Joseph (Joe) Patrick KennedyDemocrats see fundraising spike following Ginsburg death Massachusetts town clerk resigns after delays to primary vote count Bogeymen of the far left deserve a place in any Biden administration MORE III (D).

Kennedy, who is the grandson of former Attorney General Robert F. Kennedy, launched his primary challenge last month on the premise of bringing generational change to the Senate.

While early polls showed Kennedy leading Markey, the incumbent senator has racked up a number of notable endorsements in Massachusetts and Washington, including his Green New Deal co-sponsor in the House, Rep. Alexandria Ocasio-Cortez Alexandria Ocasio-CortezOn The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline McCarthy says there will be a peaceful transition if Biden wins Anxious Democrats amp up pressure for vote on COVID-19 aid MORE (D-N.Y.).

Markey also led in third-quarter fundraising, bringing in $1.1 million. Kennedy, who was in the primary race for two weeks of the third quarter, brought in $650,000.

The Massachusetts congressman has also garnered a number of labor endorsements, including the Massachusetts Laborers and the Massachusetts State Council of Machinists.