Federal and state discrimination laws have been interpreted by the courts as banning speech that creates a “hostile work environment” for members of protected classes. One example is sexual harassment. Others are racial, religious, sexual-orientation, disability, and national-origin harassment. (Some cities like Washington, D.C., Cambridge, and Boston, also ban discrimination against ex-cons, so, arguably, saying something negative about ex-cons could also be deemed “harassing”). These laws ban more speech than all other laws put together.
Eugene Volokh, a UCLA law professor, has written extensively about this issue. Today, he discusses a lawsuit against New York City and its anti-terrorism advisor for things the advisor said that offended an Arab employee who is suing the city anonymously in Doe v. City of New York. The judge ruled that any such speech could be banned if doing so was “incidental” to a general prohibition on discrimination. (See discussion here and here).
At Volokh’s web site, I comment on various statutory and constitutional reasons why the lawsuit logically should fail (but probably won’t, given the fact that judges routinely ignore limits on liability when they are angry about what they see as bigoted remarks). (See discussion here, here, here, and here).