After meeting with the board of the National Education Association (NEA) Saturday, Hillary Clinton officially picked up the endorsement of the nation’s largest labor union.

“As a lifelong fighter for children and families, I am deeply honored to have earned the endorsement of the National Education Association and their nearly 3 million members,” the Democratic presidential candidate said in a statement. “I’ve stood with educators throughout my career — from my early days working at the Children’s Defense Fund to my success creating a new teacher recruitment program in the Senate. As President, I will fight to defend workers’ right to organize and unions’ right to bargain collectively, and I will ensure that teachers always have a voice and a seat at the table in making decisions that impact their work.”

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NEA president Lily Eskelsen García described Clinton as “a strong leader who will do what is best for America’s students.”

Clinton had already secured the endorsement of the nation’s other major teacher’s union, the American Federation of Teachers.

The former secretary of state has been trying to lock down early endorsements from unions, but some are considering Vermont Sen. Bernie Sanders, who argues his agenda is better aligned with that of organized labor. Meanwhile, unions could also be torn a third way if Vice President Joe Biden enters the race. Some members of teachers unions have spoken out against their organization’s support of Clinton.

The powerful firefighters union decided to hold off on a planned endorsement for Clinton, The New York Times reported Friday, since members were not unified behind Clinton.

Sanders’ campaign responded quickly to the news that NEA had backed Clinton.

“I am proud to have the support of many hundreds of thousands of members of the National Education Association and trade unionists all across America. We are going to win this nomination and the general election because of support from grassroots Americans. We are on track to do just that,” Sanders aid in a statement.

Outside allies of the Sanders’ campaign, like the group Labor for Bernie, have been actively involved in organizing union workers on his behalf, even in organizations that have officially backed Clinton.