OP, you are in the US, you might want to think about calling the man who wrote the linked piece above. He's an SPL AND a lawyer who understands what your rights are in the workplace. Often lawyers will give free consultations. And he definitely understands stuttering, so, even tho it'd be on the phone, it'd hopefully not be too stressful talking to him? What you're going thru is unacceptable. But YOU need to know what your legal rights are and make it clear to HR that you know. Sounds like they are ignorant about this and not taking it seriously. They need to understand that they may have liability problems if they don't do what they are supposed to. Past all that... telling these asshole co-workers that you speak like this because you have a stutter which you cannot control, telling them in a calm but very direct manner, can often get THEM to fell shame and embarrassment, to apologize and back off. IF you have done that, and it has not helped, I would add that to what you might talk to this lawyer about. That's a hostile work environment and that's not legal in the US. I am really sorry you are going thru this. I hope you can find ways to make it better. You should not have to just quit.