There is also much in kind service given for legislative favor.
Take a look at any union newsletter, it is Democratic/socialist Community Organization at the Chicago level (provided as an in kind service).
Here in the Golden state, unions give a lot of $ (and presumably other methods of persuasion) support for state and local ballot propositions designed to fool voting citizens into transferring wealth and power to Dems as well. The union money does not always go to the Dems, it also goes to Dems' statist legislative propositions.
One also suspects union involvement in most of the vote fraud that goes on. Perhaps there's a dollar amount for each Dem vote created or saved, eh?
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No kidding! From "office supplies" to busing "astro-turfers" to protest events, you could probably double the cash contributions.