WASHINGTON (Reuters) - The seven Democratic candidates who have qualified for next week’s presidential debate in California threatened to skip it on Friday, saying they will not cross a picket line of union workers embroiled in a labor dispute.

South Bend Mayor Pete Buttigieg looks on as Senator Elizabeth Warren and former Vice President Joe Biden talk during a break in the U.S. Democratic presidential candidates debate at the Tyler Perry Studios in Atlanta, Georgia, U.S. November 20, 2019. REUTERS/Brendan McDermid

Unite Here Local 11, a union representing food workers at debate host Loyola Marymount University, have promised to picket the site ahead of next Thursday’s debate as they continue negotiations on a contract with Sodexo, the company that employs them.

After the union informed the candidates of the planned picket line on Friday, all of the debate participants quickly issued statements of support.

“I won’t be crossing a picket line,” former Vice President Joe Biden tweeted. “We’ve got to stand together with @UNITEHERE11 for affordable health care and wages.”

U.S. Senators Elizabeth Warren, Bernie Sanders and Amy Klobuchar, Mayor Pete Buttigieg of South Bend, Indiana, billionaire activist Tom Steyer and entrepreneur Andrew Yang also promised they would not cross the picket line.

“I take the debate stage to stand up for workers’ rights, not to undermine them,” Buttigieg said in a tweet, while Warren tweeted the union was fighting for better wages “and I stand with them.”

The Democrats are fighting for the nomination to challenge Republican President Donald Trump in the November 2020 election.

The Democratic National Committee, which sponsors the debate, said it had just learned of the issue on Friday and would never ask the party’s presidential contenders to cross a picket line.

“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,” said Xochitl Hinojosa, a DNC spokeswoman.

Sodexo did not immediately respond to a request for comment.

The union said it represents 150 cooks, dishwashers, cashiers and servers at the university who work for Sodexo, a global services company that subcontracts with the university for food service operations.

The union said in a statement it has been in negotiations since March for a new collective bargaining agreement, and the company canceled scheduled negotiations last week.

“We had hoped that workers would have a contract with wages and affordable health insurance before the debate next week. Instead, workers will be picketing when the candidates come to campus,” said Susan Minato, co-president of Unite Here Local 11.