Sara Nelson, president of the Association of Flight Attendants and a powerful leader in the labor movement, endorsed Democratic Massachusetts Sen. Ed Markey in Boston on Saturday.

Described by The New York Times as “America’s most powerful flight attendant,” Nelson is credited with helping to end the federal government shutdown last year after calling for a strike over airline safety and security concerns.

Markey has partnered with Nelson and the AFA — which represents almost 50,000 flight attendants at 20 airlines — to, among other things, ban knives on planes and ensure cargo is scanned before being loaded, according to a news release from the senator’s office.

Earlier this week, Nelson testified before the Security Subcommittee of the Senate Commerce, Science and Transportation Committee, where Markey is the ranking Democrat. She spoke on the Known Crew Member program, cyber security and airport scanning, the senator’s office said.