Controversy continues to roil this week’s upcoming Democratic presidential primary debate in Los Angeles amid an ongoing labor dispute, anger over the tightening qualification standards and discontent with Democratic National Committee Chairman Tom Perez.

The debate, which was originally slated to be held at the University of California, Los Angeles (UCLA), was moved to Loyola Marymount University after AFSCME Local 3299 – the union representing more than 25,000 University of California service and patient technical care workers – and the state school forced UCLA to inform the Democrats and its media partners to abandon plans to host the debate at the Luskin School of Public Affairs.

But another labor dispute at Loyola Marymount University is now once again threatening the December 19 debate and the top Democratic primary candidates are threatening to boycott the event if they have to cross a picket line to get to the stage.

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A labor union called UNITE HERE Local 11 says it will picket outside the event, and Massachusetts Sen. Elizabeth Warren and Vermont Sen. Bernie Sanders responded by tweeting they wouldn’t participate if that meant crossing it. Former Vice President Joe Biden, Mayor Pete Buttigieg of South Bend, Ind.; Minnesota Sen. Amy Klobuchar, environmental activist Tom Steyer and businessman Andrew Yang followed suit.

“The DNC should find a solution that lives up to our party's commitment to fight for working people. I will not cross the union's picket line even if it means missing the debate,” Warren tweeted.

Sanders tweeted, “I will not be crossing their picket line,” while Biden tweeted: “We’ve got to stand together with @UNITEHERE11 for affordable health care and fair wages. A job is about more than just a paycheck. It's about dignity.” The other candidates used Twitter to post similar sentiments.

UNITE HERE Local 11 says it represents 150 cooks, dishwashers, cashiers and servers working on the Loyola Marymount campus. It says it has been in negotiations with a food service company since March for a collective bargaining agreement without reaching a resolution, and “workers and students began picketing on campus in November to voice their concern for a fair agreement. The company abruptly canceled scheduled contract negotiations last week.”

Loyola Marymount said that it is not a party to the contract negotiations but that it had contacted the food services company involved, Sodexo, and encouraged it “to resolve the issues raised by Local 11."

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“Earlier today, LMU asked Sodexo to meet with Local 11 next week to advance negotiations and solutions. LMU is not an agent nor a joint employer of Sodexo, nor of the Sodexo employees assigned to our campus," the university said in a statement. “LMU is proud to host the DNC presidential debate and is committed to ensuring that the university is a rewarding place to learn, live, and work."

DNC Communications Director Xochitl Hinojosa said both the DNC and the university found out about the issue earlier Friday, but expressed support for the union and the candidates' boycott, stating that “Tom Perez would absolutely not cross a picket line and would never expect our candidates to, either.”

“We are working with all stakeholders to find an acceptable resolution that meets their needs and is consistent with our values and will enable us to proceed as scheduled with next week’s debate,” she said in a statement.

Perez, meanwhile, received a tersely worded letter from a number of Democratic candidates, asking him to relax the qualifications for January’s debate in South Carolina.

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“The escalating thresholds over the past few months have unnecessarily and artificially narrowed what started as the strongest and most diverse Democratic field in history before voters have had a chance to be heard.” The letter, which was signed by New Jersey Sen. Cory Booker, along with Biden, Sanders, Buttigieg, Klobuchar, Steyer, Warren, Yang and former Housing and Urban Development Sec. Julian Castro, stated.

The letter continued: “As a result, candidates who have proven both their viability and their commitment to the Democratic Party are being prematurely cut out of the nominating contest before many voters have even tuned in -- much less made their decision about whom to support.”

Given the continually escalating qualifications for the debates – and issues with fundraising – the Democratic field has already seen household names like Sen. Kamala Harris of California and former Texas Rep. Beto O’Rourke of Texas abandon their presidential bids.

“[W]hile we know this was an unintended consequence of the DNC’s actions, many of the candidates excluded due to these thresholds are the ones who have helped make this year’s primary field historically diverse,” the letter stated.

The controversies surrounding the debates and concerns over the party producing a viable candidate who can defeat President Trump in next year’s general election have cast doubts on Perez’s leadership of the party.

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In a lengthy interview with the New York Times that was published on Saturday, Perez said that the qualifications for next month’s debate were not going to change – despite the pleas from Booker – and said if voters are upset over the lack of diversity on the debate stage they should voice it when asked.

“I’m not doing the polling,” Perez said. “I’m a huge fan of Cory Booker. I think the world of him. I worked with him dating back to when he was mayor. And if voters are disappointed that he hasn’t qualified, then when they answer the phone, they need to express their preference for Cory Booker.”

Perez also confirmed that he will not be seeking another term at DNC chairman.

Fox News’ Lee Ross and The Associated Press contributed to this report.