You are correct about stuttering falling under the ADA. This can be tricky though, since "talking to people" may reasonably be considered an "essential job function" (depends on the job), in which case employers are permitted to not hire/fire someone if they cannot perform that job function. Also, in OP's case (and this may sound harsh, but is probably how it would be assessed), it sounds like *OP* is the one who is preventing himself from speaking, vs. any external pressures. If the boss or coworkers were saying, "We don't want you to talk or contribute because you stutter," that is obviously discrimination. But, if those around are pretty accepting or fine with the stutter, and it is the OP's own internal experience of stress and self-consciousness that is resulting in reduced communication on OP's part, I'm pretty sure that isn't covered under the ADA. OP, if you feel you are holding back performance-wise due to speech-related concerns, and that this may impact your perceived performance, I would strongly recommend discussing your stutter with your manager/boss (assuming you haven't already). If you disclose and let them know that speaking is really stressful for you, they may be sympathetic and find ways to allow you to thrive and be successful without stressing you out too much.