The National Education Association, the largest labor union in the country, endorsed former vice president Joe Biden for the Democratic presidential nomination late Saturday, calling him “a tireless advocate for public education” and saying members are ready “to use their power” to elect him to the White House.

Lily Eskelsen García, president of the 3 million-member teachers’ union, made the announcement just days before Florida and other key states hold primaries in which Biden faces off with his main rival, Sen. Bernie Sanders (I-Vt.), and a day before the two men are set to debate.

Eskelsen García, who had earlier she would wait to endorse to see who had the ability to attract voters, made the announcement not long after Biden’s seemingly stalled campaign got a huge and surprising boost in Super Tuesday races in early March.

After a number of key rivals ended their campaigns and endorsed Biden, he has become the front-runner for the Democratic Party’s nomination and seems close to being the presumptive nominee.

“He understands that as a nation we have a moral responsibility to provide a great neighborhood public school for every student in every Zip code,” Eskelsen García said, noting that Biden’s wife, educator Jill Biden, is an NEA member.

“With so much at stake in this election, educators are determined to use their voice to propel Joe Biden to the White House,” she said.

The union, in its endorsement statement, also noted that “NEA voters are highly reliable with turnout rates exceeding 90 percent in the most critical battleground states,” signaling it was ready to work for Biden to win the nomination and beat President Trump in November.

The decision by NEA’s leadership was certain to disappoint some of its members, who have supported Sanders. He offered an extensive education plan to boost public schools that was praised by public education advocates, and he has repeatedly said his strongest support comes from teachers.

Sanders won the endorsements recently of the United Teachers of Los Angeles, and the Clark County Education Association, the largest teachers union in Nevada. But neither of the two national teachers’ unions wound up supporting him outright, and Eskelsen García said many NEA members were behind Biden.

Eskelsen García, who has said in the past she was waiting to endorse to see who could beat Trump, praised Biden for “pledging to build the best, most innovative schools in the country, especially in low-income communities where the need is the highest.”

She praised his plans to boost public education and address racial injustice by expanding community schools — which provide students and families with wraparound services as well as academics — tripling funding for high-poverty schools, fully funding the federal law to help students with disabilities, and investing in high-quality, universal preschool for all 3- and 4-year-old children.

Both the NEA and the AFT came under criticism from some of its members in 2016 when it endorsed former Secretary of State Hillary Clinton over Sanders early in the Democratic presidential primary season.