Employment Law Questions? Ask an Employment Lawyer.
Because you are in a union, the union acts as your agent in all negotiations etc. They are free to enter agreement on yours and the other bargaining unit members behalf and do not have to get your consent to make such deals. If you are getting the wage & benefits agreed to in the primary contract, there is no violation of the law. The part that is potentially troubling about this matter is that the funds go into a slush fund. Without further expectation, it has potential for abuse because it should generally go into the union's general fund. It is potentially a LMRA violation but you'd have to essentially show the union agents were misusing the funds - for example to go on vacation.