Sen. Bernie Sanders (I-VVt.) greets the crowd at a rally last month in Phoenix. (Charlie Leight/Getty Images)

Presidential hopeful Bernie Sanders won the endorsement of a national nurses union Monday, in a sign of the divide among organized labor groups over the Democratic race.

National Nurses United, which represents 185,000 nurses across the country, announced its pick at an event in Oakland attend by Sanders, the independent senator from Vermont who has emerged as Hillary Rodham Clinton’s chief rival for the Democratic nomination.

“He can talk about our issues as well as we can talk about our issues,” RoseAnn DeMoro, the union’s executive director, said in an interview, adding that “Bernie’s issues align with nurses from top to bottom.”

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The endorsement was the first for Sanders from a national labor group. Last month, the American Federation of Teachers announced its support for Clinton, calling her “the champion working families need in the White House.”

It remains unclear whether the AFL-CIO, labor’s umbrella group, will side with either candidate during the Democratic primaries, given the division among its 56 member organizations. Both candidates, along with former Maryland governor Martin O’Malley, made pitches last month to a meeting of the AFL-CIO’s executive council in Silver Spring, Md.

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Sanders’s long advocacy of a single-payer health-care system is among the issues that resonated with the nurses union. Late last month, the senator, a self-described democratic socialist, appeared at a rally in Washington sponsored by the union and announced he would re-introduce “Medicare-for-all legislation.”

DeMoro also said that Sanders understands the threat to public health from climate change, environmental degradation and the proposed Trans-Pacific Partnership and cited several other issues on which he has stood with nurses, including support for nurse-to-patient ratios at hospitals.

“He’s unequivocal on the issues,” DeMoro said, adding that on several of the union's priorities Clinton “fell very short.”

The union said its announcement was attended by several hundred nurses at its Oakland headquarters and live-streamed to 34 watch parties in 14 states.