This is one of the factors that we are researching currently in Ohio.
You will likely find in your research that unions have reworded the standard language on the membership card that is signed and that you signature gives the union express permission to use union dues for political purposes (i.e. those political activities allowed by law such as get out the vote or contributions to political parties, but not individual candidates or PAC's. as is prohibited by law.) Most unions did this almost immediately after Beck which was quite a few years ago now.