Democratic presidential candidate Elizabeth Warren raked in tens of thousands of dollars from teachers' unions before reversing her past support for student vouchers and education reform.

In 2004, Warren argued that vouchers "relieve parents" from relying on failing public schools. Her campaign's newly-released education plan attacks charter schools and school choice. Warren's reversal comes after the Massachusetts senator took more than $2.5 million in campaign cash from the education industry throughout her political career, including nearly $70,000 from the country's most powerful teachers' unions, according to the Center for Responsive Politics.

Both the National Education Association (NEA) and the American Federation of Teachers (AFT) quickly praised Warren's plan, calling it "rooted in respect," "bold," and a "game-changer." The proposal, described as a "teachers union dream," marks yet another example of the influence public sector organized labor has on the 2020 Democratic presidential field. On Tuesday, Warren flew to Chicago to participate in a teachers strike that has affected hundreds of thousands of students.

The Warren campaign did not return a request for comment.

Labor watchdogs criticized Warren's plan for placing a priority on powerful labor lobbies, rather than children. Charlyce Bozzello, spokeswoman for the Center for Union Facts, said Warren's proposal represents a "race to the bottom" to maintain the status quo for influential teachers' unions.

"Like most labor groups that are courting 2020 Democratic presidential hopefuls, the teachers' unions are eyeing candidates who will do the most to promote their agenda," she said. "It's a race to the bottom on which candidate can best maintain the status quo for the NEA and AFT, regardless of the potential detriment to students."

Warren's proposal calls for the "aggressive oversight" of charter schools and the elimination of federal funding for them, and it opposes the "diversion of public dollars" to vouchers.

In 2004, Warren fully endorsed education vouchers, writing that they "relieve parents" from the same school systems she now supports.

"A taxpayer-funded voucher that paid the entire cost of educating a child (not just a partial subsidy) would open a range of opportunities to all children," Warren wrote in her book, The Two-Income Trap. "With fully funded vouchers, parents of all income levels could send their children – and the accompanying financial support – to the schools of their choice."

"Fully funded vouchers would relieve parents from the terrible choice of leaving their kids in lousy schools or bankrupting themselves to escape those schools," the book says.

Warren acknowledged that her proposal might meet some political opposition because "the term ‘voucher' has become a dirty word in many educational circles." Teachers' unions have long opposed vouchers and clash with charter schools that do not employ union members. Patrick Semmens, spokesman for the National Right to Work Foundation, said charter schools—and any student success in them—threatens the monopoly many unions have on the education industry.

"Teacher union bosses hate charter schools because they are a challenge to their monopoly over education and because union organizers have largely been unsuccessful in convincing charter schoolteachers to join unions," Semmens said. "It's no surprise that politicians looking for Big Labor's political backing feel the need to denounce charter schools, even when their past statements suggest they know better."