Many of these groups have primarily focused on mobilizing their millions of members — and spending significant sums of money — for their preferred candidate in the Democratic primary thus far. The letter recognizes a significant shift in thinking among them, with leaders in the party’s left wing now setting their sights more squarely on Trump rather than the protracted battle between Clinton and Sanders. The signatures are acknowledgments from leaders of those organizations that the time has come to more seriously confront Trump — who could, they warn, actually win.

“Today we are calling for a massive nonviolent mobilization of working people, students, immigrants, children of immigrants, great-great-grandchildren of immigrants, people of color and white people, the unemployed and under-employed, people of faith, retirees, veterans, women, and men — anyone who opposes bigotry and hate and loves freedom and justice — to stand up to Trump’s bullying and bigotry,” the note continues.

Other high-profile signers of the letter — which was set to be released in the opening hours of voting on Tuesday as Ohio, Illinois, Missouri, North Carolina, and Florida go to the polls — include Michael Brune, executive director of the Sierra Club; Ilyse Hogue, president of NARAL Pro-Choice America; Annie Leonard, executive director of Greenpeace USA; and May Boeve, executive director of 350 Action. The text encourages more groups to sign onto the effort.