Can you better define warning? Was it worded as a warning, or was it a coaching? Regardless, contact HR and tell them you have a disability. Explain your concern that your manager might not have a proper appreciation for your condition. Don't cast any shade at the manager. Just communicate your concerns. HR isn't on your side, per se, but neither are they on the manager's side. After speaking to HR, see if they have a solution. One thing HR might suggest is that your manager coach you on how to "pick up your numbers." In addition to managers setting expectations, they should help you achieve them. Maybe your manager doesn't understand stuttering as a condition / disability. Are you adhering to the new workflow, to the best of your ability? Is your stutter the only thing interfering with you achieving the desired metrics? What numbers are they seeking that you improve? Is it a call center? I worked in a decent sized call center. As both a CSR and as a quality manager. (I actually found that talking on the phone as a CSR was great for my fluency. Granted I had already achieved good fluency via speech therapy, but for me, practice is key for continued fluency.)