19 of Sanders's top 20 donors are unions. The one non-labor group on the list is the American Association for Justice, an interest group for plaintiff's attorneys, perhaps the most reliable non-union Democratic constituency. This isn't too surprising. Sanders is, along with Sen. Sherrod Brown (D-OH), just about the most pro-labor member of the Senate. He has fought free trade agreements for decades and is a major opponent of the Trans-Pacific Partnership, he's critical of guest worker programs that he believes undercut Americans' wages, and he's pushed back on the Obama administration's education reform agenda.
(Vermont, it should be said, is the only state in the union without charter schools.)