What most union members do not realize and probably are not informed of is that they can request a refund on that portion of their dues that are spent on political donations. I always did and received my refund usually accompanied by a surly attitude from the treasurer. It always made my day.
Although at least 40 percent of union members would never vote for a stinking dumycrat, very few ever request the refund, because it is more trouble than it is worth. A fair law would be one that would deny the use of union dues for any political purpose, but that would require any funds used for that purpose to be a voluntary donation, totally separate from dues. The same rule should apply to other organizations that collect dues and are not specifically political in nature.
Some will say that then those same restrictions should be applied to businesses--in particular, corporations. There is an enormous difference, but yeah, if it would stop the abuse of union members dues and other organizations from donating to politics, go ahead and make all donations personal. This of course would have to be run through the Supreme Court process, which would mean it would be subject to change, depending on the flavor of the court.