On Thursday, the American Postal Workers Union announced that it would be endorsing Democratic Presidential candidate Bernie Sanders. The union, which represents approximately 200,000 workers, is the largest labor union to back Sander's campaign. This endorsement comes just before the Democratic debate, which will happen in Iowa on Saturday. Sanders has been trying to compete with presidential candidate Hillary Clinton who has received quite a few endorsements from labor organizations.
See "Postal Workers' Union Endorses Bernie Sanders for President", November 12, 2015