First Amendment laws do not apply, but there are discrimination laws that might. Take a look at George Carlin's seven banned words (ok, I'm dating myself). Most of those words were of Anglo-Saxon or old English derivation that were banned by the ruling Norman royalty in their courts after they invaded England because they were the language of the 'common people', or the vulgarus.
Oppressing a group's language and deeming it offensive and making it illegal/forbidden is about as discriminatory as you can get. If it is legal to say 'defecate', then one must be able to say 'shit'.