It is illegal to treat an employee adversely because that employee is disabled. If you are able to perform your job well, have never had negative reviews, and now are receiving negative reviews and harsher treatment because you are disabled and for no other reason, that would be a violation of the law. The question at this point would be one of damages. Unless you are fired or suffer some other quantifiable financial loss as a result of this disability discrimination, your only recoverable damages are for emotional distress. I realize that the poor reviews and criticism you have received have been very difficult for you, but the standard for proving emotional distress is rather high, especially with today's juries who tend to be very skeptical of such claims.
For this reason, the best course of action at this stage is typically not to initiate legal action but to instead report your suspicion of disability discrimination to your boss's boss, or to the HR department if there is one. The report should be in writing--that way there is proof it was made--and it should outline the specific conduct that you believe is discriminatory and why you believe the motive is your disability.
Complaining about disability discrimination is a form of legally protected activity. What this means is that your employer will be legally prohibited from retaliating against you because you complained, and any adverse employment action which you can link to the filing of your complaint with give rise to an entirely separate legal claim for damages.
If and when it becomes time to take legal action, the first step is a complaint to the Equal Employmnt Opportunity Commission. This is actually a legal requirement before initiating a lawsuit. The EEOC will investigate and attempt to mediate a resolution with your employer. That not forthcoming, they will either file a lawsuit on your behalf or issue you a "right to sue" letter, which will enable you to sue in civil court with the assistance of an attorney.
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