Sen. Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE's (I-Vt.) support for his signature “Medicare for All” proposal has created an unexpected divide between the White House hopeful and his usually reliable labor union base.

Sanders faces scrutiny from the powerful Nevada Culinary Workers Union, which is warning that his goal of overhauling the nation’s health care system would put an end to private plans for union members.

But the labor group stopped short of endorsing one of Sanders’s Democratic rivals. On Thursday, the union declined to back a candidate, leaving the field wide open for the remaining contenders heading into the state's Feb. 22 caucuses.

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Union Secretary-Treasurer Geoconda Argüello-Kline did not directly attack Sanders when pressed repeatedly at a press conference, saying only that the union believes people have the right to make their own health care choices.

The union is a key force in elections in the state and is a highly sought-after endorsement on the road to the White House. The labor group for hospitality workers has a reputation for funding a massive turnout effort and can be a game changer, especially for a candidate seeking support from Latino voters.

On the flip side, any negative messaging from the group could pose a setback for a campaign.

The union endorsed then-Sen. Barack Obama Barack Hussein ObamaThe Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon Trump appointees stymie recommendations to boost minority voting: report Obama's first presidential memoir, 'A Promised Land,' set for November release MORE (D-Ill.) ahead of the state’s 2008 caucuses, but did not endorse a candidate in 2016. Former Secretary of State Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE won the caucuses in 2016, with Sanders a close second at 47 percent.

While the union has once again decided against endorsing a candidate, Sanders nonetheless took a hit.

Earlier this week, the Culinary Union distributed a flyer to its 60,000 members that said his health care plan would “End Culinary Healthcare.” Under Medicare for All, private health insurance would be replaced across the board with a government-run plan.

The Culinary Union drew swift backlash online from Sanders supporters, so much so that the group issued a statement on Wednesday denouncing the candidate’s backers for "viciously" attacking the union.

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That, in turn, prompted many of Sanders’s opponents to seize momentum on the public feud.

“I stand with the working men and women of @Culinary226 because supporting labor means supporting our unions,” tweeted former Vice President Joe Biden Joe BidenCast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response Biden tells CNN town hall that he has benefited from white privilege MORE, an opponent of Medicare for All.

Fellow moderates Sen. Amy Klobuchar Amy KlobucharEPA delivers win for ethanol industry angered by waivers to refiners It's time for newspapers to stop endorsing presidential candidates Biden marks anniversary of the Violence Against Women Act, knocks Trump and McConnell MORE (D-Minn.) and former South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBogeymen of the far left deserve a place in any Biden administration Overnight Defense: Woodward book causes new firestorm | Book says Trump lashed out at generals, told Woodward about secret weapons system | US withdrawing thousands of troops from Iraq A socially and environmentally just way to fight climate change MORE, fresh off strong showings in the New Hampshire primary, also jumped to the union’s defense.

“I stand with @Culinary226 and let's be clear: attacks on the union are unacceptable. I come from a family of proud union members and I know when unions are strong, America is strong,” Klobuchar tweeted.

Buttigieg, meanwhile, took the opportunity to appeal to unions and promote his own health plan.

“There are 14 million union workers in America who have fought hard for strong, employer-provided health benefits,” Buttigieg tweeted. “Medicare for All Who Want It protects their plans and union members' freedom to choose the coverage that's best for them.”

Even Tom Steyer Tom SteyerTV ads favored Biden 2-1 in past month Inslee calls Biden climate plan 'perfect for the moment' OVERNIGHT ENERGY: Trump administration finalizes plan to open up Alaska wildlife refuge to drilling | California finalizes fuel efficiency deal with five automakers, undercutting Trump | Democrats use vulnerable GOP senators to get rare win on environment MORE joined the fray on Thursday, releasing a statement calling on Sanders to disclose the price tag of Medicare for All. Steyer said his own proposal would “protect the the health plans that unions have fought hard to secure for their members, especially here in Nevada.”

Sanders has been trying to smooth over some of the tensions between the union and his supporters ever since news of the union’s flyer was first reported by the Nevada Independent.

Sanders's campaign initially responded to the flyer by saying it was incorrect and that Medicare for All coverage would be as good or better than what unions currency receive.

Sanders has noted his Medicare for All bill includes a provision that would enable companies to push savings they obtain from Medicare for All to workers in the form of either higher wages or other benefits. But some unions have been skeptical.

In an interview with MSNBC’s Chris Hayes on Wednesday, Sanders touted his labor bona fides.

“I have a lot more union support than Pete Buttigieg has or I think ever will have,” Sanders said, adding that “many, many unions in this county ... absolutely understand that we have to move to Medicare for All.”

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Sanders said in a statement the following day that he agreed with the Nevada union's key goals.

"As someone who has the strongest lifetime pro-labor record of anyone in Congress, I would never do anything to diminish the health care that unions and workers have fought for," he said.

Sander also addressed the online harassment from some of his supporters.

"Harassment of all forms is unacceptable to me, and we urge supporters of all campaigns not to engage in bullying or ugly personal attacks," he said. "We can certainly disagree on issues, but we must do it in a respectful manner."

Sanders enjoys the most labor support of all the 2020 Democratic candidates, with more than 15 endorsements, including National Nurses United and Postal Workers Union, as well as a handful of local chapters of Unite Here, the national organization of Nevada’s Culinary Union.

National Nurses Union cited the Medicare for All plan as one of the reasons for its endorsement.

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Yet while some unions have supported the ambitious health care overhaul, others are not on board.

The Culinary Union plays a unique role in its members’ health care, and there are concerns about the role it would play under a Medicare for All system.

Union members receive insurance through a nonprofit trust, funded mainly by the employers under contract with Unite Here unions — like casinos and hotels. It offers coverage for more than 130,000 members and their dependents.

At Thursday's press conference, Argüello-Kline held back on further criticisms of Sanders and instead referred back to the flier describing the candidates' positions.

“We will endorse our goals, we’re not going to endorse a political candidate,” Argüello-Kline said. “We respect every single political candidate right now.”