Maurice Mitchell, the national director of the Working Families Party, said his group will hold a call at 8 p.m. Monday with former Warren supporters to try to persuade them to switch their vote to Sanders. It will feature elected officials who had been with Warren but are now planning to cast a ballot for Sanders.

“Bernie Sanders will fight for a Green New Deal, universal health care and a living wage for every worker. Organized capital won’t rest and neither will we,” he said in a statement. “We said from the very beginning that there were two progressive champions in this race, and that our North Star was to elect one of them as president. Now, the Working Families Party will marshal its grassroots supporters and staff to help Sen. Sanders win the nomination and defeat Donald Trump.”

The Working Families Party argued that Biden’s previous support for the Iraq War, 1994 crime bill and bankruptcy legislation are “at direct odds” with its organizational values.

The endorsement comes ahead of Tuesday's Michigan primary, a potentially do-or-die contest for Sanders where polls have showed him trailing Biden by more than 20 percentage points.

Asked if he has been in touch with Warren, Mitchell said the Working Families Party has told her team that it is backing Sanders.

Beyond that, "I haven't spoken to her, but I plan on speaking to her sometime soon. We'll talk about a number of things,” he said.