I met a jerk yesterday who proudly told me he sued companies (workmans comp) by pretending injury, for a living, and ticked off the many 50K+ settlements he had gotten.
It is unfortunately Federally illegal to deny employment based on prior union membership. It is not, however, illegal to deny employment based on what political party they are a member of or how they voted in the last election. (It is illegal to make their continued employment after they are hired conditional on how they vote, though.)