Unions don't control as much money by definition. Any Union's coffers are pulled from dues coming out of the pay of the workers. While theoretically, a Union may make more than the employees of a particular Union workplace, it would be only because you took into account cash flow from other Union workplaces.
Statistical multiplexing is the only thing that makes unions viable to my understanding, and I may be wrong on that, as warchests may be partitioned by workplace, I can't confirm whether or not that is the case.
This is also one of the reasons why I'm not sold on the illegalization of secondary strikes. Labor should absolutely exploit network effects to make up for the fact that the capital class will pretty much by default.
Check out the lists of top political donations some time - e.g. on https://www.opensecrets.org/. Unions have tons of money, and they spend it lavishly on lobbying, political donations and PR.
