Most union members are forced to pay dues - they have no choice. But many are not liberal Democrats. Why should money be taken FROM them, and then used AGAINST them to further liberal ideals the dues payer is opposed to? It is morally wrong to force someone to do something that is designed to do him harm. But that is the least of it.
A majority of Americans think abortion is wrong, so it stands to reason that a majority of union members feel that way. When they are forced to pay for advocating abortion, the courts have already ruled that is unconsttutional, particularly if the person objects to abortion on religious grounds. A person cannot be forced to violate his religion. Yet, unions pay out millions in union dues to elect people who will advocate for abortion, and many other issues that violate some peoples' core beliefs. That is in direct opposition to our rights.
Here is the short take -- this is exactly the same as if the government were to impose a tax on Christians to be used to destroy Christianity.
At the very least Congress should pass a law that states each union member may choose to disallow any portion of his or her dues to be used to fund any political campaign or agenda.
I will tell you, if I were in a union by force, and forced to pay dues, I would sue the unions for violating my First Amendment rights. The Constitution is clear - a person's religious beliefs are sacred and must not be infringed.