Hard to say, but I know dues are supposed to be 2.5 hrs of pay per month. Sometimes payroll screws things up and doesn't take out dues when they are supposed to, then they take out extra to get you caught backup. Check prior pay stubs to make sure this isn't happening, then figure out what 2.5 hours a month would be for you and be sure that they aren't taking out extra by mistake. If so I believe there is a way to get a refund from the union, and your local hall should be able to help you with it. I've known this to happen to only one other person before.
The next pay where union dues were taken out of my pocket, the dues went down by 10% which brought my dues to exactly 2.5 hours pay. Then this last pay the union refunded 4% of the total they have taken from me this year.