https://www.americanprogressaction.org/issues/labor/news/2014/11/14/101163/unions-are-among-the-very-few-interest-groups-that-represent-the-middle-class-2/
"Buried deep inside Princeton University political scientist Martin Gilens’ research highlighting the excessive influence the rich have on modern U.S. politics, there is a hidden gem exploring which interest groups best represent the priorities of the middle class. Gilens found that, while most powerful interest groups advocate for policies that predominately benefit their narrowly defined members, relatively few focus on policies that the middle class supports. According to Gilens, most of these middle-class oriented groups are unions"
