A union that represents 15,000 health care workers in California – the largest state to vote on Super Tuesday next March – is splitting its endorsement between Sens. Bernie Sanders and Elizabeth Warren, the two populist standard-bearers in the race for the Democratic presidential nomination.

The National Union of Healthcare Workers – which backed the independent senator from Vermont in his 2016 Democratic presidential primary bid – announced on Thursday that they’ll provide resources and grassroots support to both Sanders and Warren.

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The union explained that the gap between Warren and Sanders in a vote by union members was close enough that the union’s executive board decided on Wednesday to endorse both candidates.

“This is not your typical union endorsement. We didn’t tell our members how to vote, they told us,” union president Sal Rosselli said. “We trust our members and their judgments and the outcome of this vote reflects the collective will of members from San Diego to the Oregon border. Our members clearly like both Senators Warren and Sanders.”

“After reviewing the vote totals, our executive board felt that an endorsement of both candidates was most fair due to the closeness of the vote,” he explained.

Union members voted from Sunday through Wednesday, with members able to cast a ballot for up to three candidates. Warren received the most votes, appearing on 61 percent of ballots, with Sanders showing up on 50 percent of ballots.

Home-state Sen. Kamala Harris appeared on 34 percent of ballots. She was endorsed by the union in her races for California attorney general and her 2016 election to the U.S. Senate. Former Vice President Joe Biden was fourth in the voting, showing up on 32 percent of ballots.

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The splitting of the endorsement comes as some in the Sanders campaign are starting to take aim at Warren. Both Sanders and Warren have – to date – refrained for criticizing each other.

But new national and early voting state polls released over the past week indicate Warren soaring into a tie with long-time front-runner Biden for the top spot in the 2020 Democratic battle, with Sanders dipping to third.

Earlier this month Warren landed the endorsement of the New York-based progressive group the Working Families Party, which backed Sanders four years ago in his first White House bid.