Literally. From a report by the Treasury Department:

Unionization also has spillover effects that extend well beyond union workers. Competition means workers at nonunionized firms see increased wages too. Heightened workplace safety norms can pull up whole industries. Union members improve their communities through heightened civic engagement; they are more likely to vote, donate to charity, and participate in a neighborhood project. And, the higher pay and job security of both union and nonunion middle-class workers can further spill over to their families and communities through more stable housing, more investment in education, and other channels.