The Nevada union, with outsized influence in a state heavily dependent on tourism, is against Sanders' Medicare for All plan, a government takeover of healthcare that would end private healthcare insurance.
The union is concerned with the potential loss of the health care benefits it has negotiated with employers under the rollout of a government-run health care program that would abolish private insurance.
When reached by text message, Bethany Khan, a spokesperson for the Culinary Union, said the attacks were coming over the phone and social media. "We know they are great people", said Geoconda Argello-Kline, the union's secretary and treasurer.
But the Culinary has been making Sanders seem a little scary. It's not the first time the two camps have clashed.
At a December town hall event with the Culinary Union, Sanders was heckled by some members of the crowd when discussing single-payer health care.
She continued, "Bernie has been clear that under Medicare for All, we will guarantee that coverage is as comprehensive or more so than the health care benefits union workers now receive, and union health clinics, including the Culinary's health clinic, will remain open to serve their members". The leaflet did not explicitly name any candidates.
In a statement to CNN, Sarah Michelsen, Sanders' campaign director in Nevada, made note of the senator's career, saying he "stood with workers ... fighting on picket lines against pension cuts and corporate greed".
The Culinary Union is Nevada's largest immigrant organization with members who come from 178 countries and speak more than 40 different languages.
"We respect every single political candidate right now".
She said the union will "really work hard" to defeat President Donald Trump in 2020. Nearly every major Democratic candidate still in the race has spoken to union members in the past year.
The non-endorsement from the union is another example of opponents of Sanders - or of parts of his progressive policy platform - failing to coalesce around a more moderate alternative.
Former Vice President Joe Biden, the one-time front-runner who finished a disappointing fourth in Iowa and fifth in New Hampshire, referred to the union's statement in a tweet and said, "supporting labour means supporting our unions".
After the chaotic Iowa caucuses, all eyes are on Nevada, which begins early caucus voting on Saturday.