Even though union dues are compulsory, it is legal for unions in Pennsylania to use them to support candidates (though contributions directly to candidates and paid TV advertising is prohibited under federal and state law). In compulsory union states like Pennsylvania, individuals would have to opt out of union membership to avoid the portion of dues used for politics (they would still have to pay the agency fee). Union members who don’t want to see their dues used to support Obama or other PSEA endorsed candidates should see the National Right to Work guide on how to do this.
Several states have passed paycheck protection laws, which grant union members the right to refuse to contribute to political efforts of the union. PA Right to Work has a survey asking state lawmakers and legislative candidates if (among other things) they support paycheck protection legislation.
Also visit UnionFacts.com for more on how union dues are used for politics.