The American Federation of Teachers endorsed Hillary Clinton for president on Saturday.

AFT, which boasts 1.6 million members, said it was the first major union to endorse a Democratic candidate in the 2016 election cycle. AFT is the second largest teachers’ union in the country.

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“In vision, in experience and in leadership, Hillary Clinton is the champion working families need in the White House,” AFT president Randi Weingarten said in a statement. “Hillary Clinton is a tested leader who shares our values, is supported by our members, and is prepared for a tough fight on behalf of students, families and communities. That fight defines her campaign and her career.”

On values, strength and personal support, our @AFTunion members overwhelmingly supported endorsing @HillaryClinton http://t.co/n85FuEdTVY — Randi Weingarten (@rweingarten) July 11, 2015

Clinton said she was “honored” to win the group’s endorsement.

AFT endorsed Clinton in 2008, and Weingarten is a longtime Clinton ally. Last year, Weingarten joined the board of the main super PAC supporting Clinton.

Clinton, along with Democratic candidates Sen. Bernie Sanders and former Gov. Martin O’Malley, met with the union’s leaders last month in Washington, D.C., in an attempt to clinch the group’s endorsement.

“What you saw, bottom line, is that the three candidates talked about a reset of education policy in america,” Weingarten told msnbc’s Richard Lui in early June. “… Over and over and over again, all three of them talked about how, in Hilary’s words, teachers cannot be scapegoats for society’s problems; in Martin O’Malley’s words – and he has a daughter who teaches in Baltimore – you can’t vilify teachers; in Bernie Sanders’ words, he wants a political revolution because it’s time to stop having this kind of cutting, cutting, cutting of public education.”

Teachers unions have lately found themselves in the crosshairs of many education reform activists and Republicans, who see the unions as caring less about educating children than protecting themselves. Reformers tend to favor charter schools, which are often not unionized, along with stricter teacher testing standards, and less employment protection for educators.

Alex Seitz-Wald contributed.