From Politico:

Three prominent liberal activists — including the president of a large union — are calling for Elizabeth Warren to challenge Hillary Clinton for the Democratic presidential nomination, insisting that the Massachusetts senator’s participation in a competitive primary process would benefit the party.

Warren hasn’t budged from her insistence that she won’t pursue a White House bid. But the new voices calling for her candidacy represent a new phase in the progressive push to persuade her to run, just days after Clinton appeared alongside two other union chiefs on a panel in Washington — and not long before Clinton is expected to launch her long-anticipated presidential bid.

“We agree with former Labor Secretary Robert Reich, the Boston Globe, and many others that Sen. Elizabeth Warren would be a strong candidate, and that if Hillary Clinton also declares, the debate between the two of them would be critical for our nation,” write Larry Cohen, president of the Communications Workers of America, and Annie Leonard, executive director of Greenpeace USA — the environmental group — in a new letter published by Run Warren Run, a campaign organized by liberal political organizations.