Democratic 2020 U.S. presidential candidate and U.S. Senator Bernie Sanders (I-VT) speaks at a campaign stop in Hooksett, New Hampshire, September 30, 2019.Brian Snyder | ReutersAll of the 2020 Democratic presidential candidates threatened Friday to skip next week’s debate as they pledged support for workers in a contract dispute at the university where it will take place.The seven contenders who qualified said they will not cross a picket line at Loyola Marymount University, where the Democratic National Committee will hold Thursday’s debate. UNITE HERE 11, a culinary union that represents 150 workers at the university, said it will boycott the event after negotiations with food services company Sodexo fell apart. Sodexo employs those workers at the school.Sens. Elizabeth Warren, D-Mass., Bernie Sanders, I-Vt., and Amy Klobuchar, D-Minn., former Vice President Joe Biden, South Bend, Indiana, Mayor Pete Buttigieg, entrepreneur Andrew Yang and billionaire activist Tom Steyer threatened to sit out the debate.”The DNC should find a solution that lives up to our party’s commitment to fight for working people,” Warren, the first candidate to voice support for the union Friday, wrote in a tweet. “I will not cross the union’s picket line even if it means missing the debate.”The other six candidates in the debate followed in saying they would not cross the picket line at Loyola Marymount.UNITE HERE 11, which represents about 32,000 hospitality workers in southern California and Arizona, said workers started picketing at Loyola Marymount last month. Sodexo canceled scheduled negotiations last week, the union said.In a statement, a Sodexo spokesperson said the company is “100% committed to reaching an agreement, and any statement that we have left the bargaining table is not accurate.” The spokesperson added that the company “has been negotiating in good faith” with the union for about a year.The DNC had to change the debate location once already. The party moved the event from the University of California, Los Angeles due to a labor dispute at that school.The DNC and Loyola Marymount did not immediately respond to requests for comment.Democrats have angled for endorsements from organized labor, a key constituency for the party. UNITE HERE has a large footprint in Nevada, one of the first four nominating states in the Democratic primary process.The union held Las Vegas town halls this week with Biden, Warren and Sanders.Subscribe to CNBC on YouTube.