7. International Brotherhood of Electrical Workers
Dating back to 1891, the IBEW is exactly what it says it is, a union representing electrical workers in the U.S., Canada and parts of the Caribbean. Its members come from highly skilled fields, working in utilities, broadcasting, manufacturing, railroads, telecommunications, and construction, to name a few. Cash contributions to Democratic campaigns by the IBEW total almost $33 million since 1989, the second-highest dollar amount among all unions.
Sticking it to the man: In 1919, IBEW leadership co-founded the Council on Industrial Relations, an arbitration board established to settle labor disputes before they blew up into major crises. In doing so, the IBEW and management nipped several potential strikes in the bud, making for a smooth, cooperative relationship compared to their peers in other industries.