When my mother was a school teacher, the union had mandatory fees which went to partisan political campaigns against her ideology and self interest. I think this was eventually challenged and overturned in court, but it left a terrible impression.
This is my biggest gripe with unions in the US: that they can basically force you to join the union against your will if you want to perform certain jobs. The Teacher's Union is notorious for this.
There was a fairly recent ruling from the SCOTUS that struck down compelling non union members to pay union dues. It was as recently as 2018 or 2019. Cant remember the case name, but it originated in Illinois (a very, very pro union state).
