Thank you for your reply. I understand that you are based in AZ and will answer your question based on AZ law.
The general rule in AZ is that employment is "at will" absent an express agreement to the contrary. At will employment can be terminated or modified for any reason not amounting to discrimination on the basis of a legally protected trait (race, religion, gender, etc.) or retaliation for engaging in certain forms of legally protected conduct (filing a wage claim, taking FMLA leave, etc.). It doesn't matter whether the basis for termination/modification is fair, reasonable or even true.
Since employment is at will absent an agreement to the contrary, no law regulates or limits an employer's ability to implement PIPs, discipline, or other remedial programs for their employees. Indeed, such restrictions would not make sense if the employer can simply fire or demote an at will employee without cause or reason.
I asked what the nature of your complaint was about your boss because certain complaints are "legally protected activity." However, complaints about your boss's communication skills, professionalism, and tendancy to be judgmental would not fall within that category. In other words, you do not have a legally protected right to complain about these things and your employer is completely free to retaliate against you because of such complaints.
You mention that you had a stroke. If you can prove that you are now being targeted BECAUSE of the medical condition which led to the stroke (i.e. your employer wants to get you out because they fear their health insurance premiums will go up, or because you will miss work in the future), that would constitute discrimination on the basis fo a legally protected TRIAT (disability) and thus be actionable. However, you would need to prove that this was your employer's motive, and you would need specific evidence of that to meet your burden of proof.
If you believe there is evidence to suggest that this is your employer's motive, your recourse here would be to file a complaint with the Equal Employment Opportunity Commission. That is the federal agency that enforces the federal anti-discrimination laws. 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.
In any case, since filing a complaint with the EEOC is a form of legally protected activity, your employer will be much less likely to terminate you or demote you out of fear that it will be seen as retaliation for your EEOC complaint.
In summary, the complaints you describe yourself as having made are not legally protected, which means your employer can lawfully retaliate against you for them. However, since disabilities are legally protected traits, it would be illegal for your employer to target you with a PIP if that was their motivation for doing so. You would need to prove that motive, but you may wish to file a complaint with the EEOC, who can investigate. An EEOC complaint will also make your employer less likely to take adverse action out of fear it will be seen as illegal retaliation.
I hope that you find this information helpful. Please do not hesitate to let me know if you have any questions or concerns regarding the above and I will be more than happy to assist you further.
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