The Nevada caucuses, which are the third presidential Democratic nominating contest, are less than six months away, and Democratic presidential candidates are ramping up efforts to court a mammoth Las Vegas labor union that has played an important role in the caucus outcome in the past.

Claiming to be "one of the strongest political forces in the state," the Culinary Union has only rarely shied away from wielding its influence in Nevada. Its 60,000 members work at the heart of the state's economy: the gaming and tourism industry.

With what is currently the largest primary field in recent history, a split outcome in the first two contests in Iowa and New Hampshire would leave a big opening for a presidential hopeful in Nevada. The union's endorsement in the 2008 caucuses — Nevada's first as an early deciding contest — was seen as a pivotal boost for then-candidate Barack Obama, though insufficient to deliver a majority of the state's precincts. Still, while Clinton won the state, Obama took more delegates because of the way Nevada apportions them.

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"We were the first union who endorsed President Obama, and we feel proud about that," Geoconda Arguello-Kline, secretary-treasurer for the Culinary Union told CBS News.

In 2016, the union sat out the contest amid a pitched battle in the state between Hillary Clinton and Bernie Sanders.

This year, the labor heavyweight has not ruled out a 2020 endorsement and will be looking a number of issues, including wages, healthcare, and immigration.

But there is also another factor that might hold some sway in the union's decision: the Culinary Union's years-long fight with Station Casinos, a local casino and hotel chain.

The Culinary Union has accused Station Casinos of ignoring successful elections to unionize at several of its twenty locations and stalling talks at some properties through costly court appeals. It also points to past accusations that workers were harassed and retaliated against over their labor organizing.

"Right now, the Station Casinos are sending the message that they don't respect the democratic process," said Arguello-Kline.

In May, the National Labor Relations Board, which is now under Republican control, ruled against Station Casinos for its "unlawful failure and refusal to recognize and bargain with the union" at the Palms. Station Casinos is appealing the decision.

"[O]ur challenges are both legal and appropriate," Michael Britt, senior vice president of government relations and corporate communications for the company, told CBS News in a statement.

The campaigns of Joe Biden, Cory Booker, Pete Buttigieg, Julián Castro, Kamala Harris, Amy Klobuchar, Beto O'Rourke, Bernie Sanders and Elizabeth Warren — have all voiced solidarity with the Culinary Union in its fight, calling on Station Casinos management to negotiate with the union.

Staff for Booker, Buttigieg, Castro, Harris, Klobuchar, and Sanders have also told CBS News that their campaigns have steered clear of all Station Casinos properties in Las Vegas, which has no shortage of hotels. These campaigns also say they have received no donations from the company's leadership.

"It's time for the Palms' billionaire, Trump-supporting owners to stop ignoring the law and start negotiating with their workers," Sanders posted in August.

And as the Culinary Union's distinctive red shirts — some reading "WE VOTE WE WIN" — have turned up at a number of candidates' campaign stops, organizers from a number of campaigns have turned out for the union's high-profile demonstrations outside Station Casinos properties. Here, Gabe Uy, the political director for Harris' campaign in Nevada, tweeted from one protest:

But a handful of candidates who say they stand with the Culinary Union may have also run afoul of the group, CBS News has learned, by patronizing a Station Casinos property or accepting money from one of its executives.

Federal election filings reveal that Sen. Elizabeth Warren's campaign, which had vowed to "stand with the Palms workers" as early as March, has repeatedly crossed the picket line at the Palms Casino Resort, which is in the crosshairs of the union's boycott, with stays in May and June. Candidate Marianne Williamson also stayed at the Palms in May.

A Warren campaign spokesperson told CBS News that the incident in question involved two advance staff members and claimed that there was no picket line. The spokesperson says the campaign apologized to the Culinary Union "weeks ago when we realized it."

"Keep the pressure on. Shoulder-to-shoulder, I'm in this fight with you and the Culinary Union all the way," Warren had said in a video posted last week.

In a statement to CBS News, Williamson reiterated her support for labor unions, citing "travel and scheduling restrictions" for the booking.

"We were relegated to visiting the Palms Casino and Resort, where we had a terrific experience in large part to the pro-union staff," writes Williamson, adding that she urges the company to "set an example of social responsibility in business."

"If you stay in these places, you don't respect these workers when they work through a democratic process," Geoconda Arguello-Kline, Secretary-Treasurer for the Culinary Union, tells CBS News.

"We believe that candidates saying they are fighting for the working class, they are not going to be at the Station Casinos," she added later.

As Sanders has noted, the company's owners are frequent donors to the president and Republican causes. But at least one board member, Dr. James Nave, has also given generously to several Democrats, including a $5,600 donation to Joe Biden's campaign, which has heavily outraised rivals in southern Nevada.

Arguello-Kline called on all Democrats to return donations from Station Casinos executives.

"I think anybody who receives donations from an anti-union company, a union-busting company, that doesn't respect the democratic process. They have to return that money," said Arguello-Kline.

"We're proud of all the contributions we've received in Nevada — 95 percent of which were 200 dollars or less," Vedant Patel, communications director for Biden's campaign in Nevada, told CBS News, declining to comment on specific donations. He also said that Biden "has long been a champion for organized labor."