Your question ("What can I do?") is far too involved and fact-contingent to provide a competent answer on this limited and PUBLIC online forum.
A few things for you to keep in mind:
The law imposes no inherent obligation of "fairness" in the workplace. Adverse employment action is illegal only if motivated by a legally protected trait (race, religious creed, color, national origin, ancestry, physical disability, mental disability, medical condition, marital status, sex, age, or sexual orientation) So, your employer is free to fire you or demote you on the basis of false allegations and the courts will not intervene. (You may, however, have a cause of action for defamation against the person or persons who told lies about you).
Likewise, generally rude or offensive behavior will constitute unlawful "harassment" only if the basis for such harassment is one of the legally protected traits mentioned above. So for example, while it's illegal to yell racial slurs at any employee, it is not illegal to call them stupid.
Unless you are a union member or have a contract guaranteeing your employment for a specified term, you are an "at will" employee and as such can be terminated for any reason not expressly prohibited by law. Termination may be "wrongful" in the sense that it is unfair or even unethical, but that does not make it legally actionable.
What you should gather from this is that employers enjoy tremendous discretion to manage their business as they see fit and employees generally have few employment rights. This is not to say you have no legal claim or claims. I am in no position to make that determination. Given the complexity of your specific circumstances, you would strongly benefit from a more detailed consultation with a local employment law attorney.
This answer is a general interpretation of the law and is not fact specific to your case. Likewise it does not create an attorney-client relationship. You should seek an attorney for a review of your specific facts and documents.
Most forms of workplace harassment are perfectly legal and do not give rise to a meritorious cause of action. The only harassment that is unlawful is harassment directed at the employee because the employee is a member of a protected class of people, or because the employee had engaged in some form of legally protected conduct. All other forms of what you might call harassment, including rudeness, favoritism, nepotism, unreasonable expectations, and irrationality do not give rise to any claim of wrongdoing.
That said, if you become disabled from doing your job as a result of such conduct, and you can prove the disabling condition is work related, you may be able to file a workers compensation claim seeking treatment and temporary disability benefits.
Get a workers compensation attorney immediately, and follow his or her advice, not the advice of your employer or the employer's doctor.
Good luck to you.
This answer should not be construed to create any attorney-client relationship. Such a relationship can be formed only through the mutual execution of an attorney-client agreement. The answer given is based on the extremely limited facts provided and the proper course of action might change significantly with the introduction of other facts. All who read this answer should not rely on the answer to govern their conduct. Please seek the advice of competent counsel after disclosing all facts to that attorney. This answer is intended for California residents only. The answering party is only licensed to practice in the State of California.
Harassment is only unlawful if it is based upon a protected characteristic, and is severe and pervasive, giving rise to a hostile work environment and/or if there is quid pro quo harassment. In addition, defamation is only actionable under specific rare circumstances, typically not in the work place, where employers are privileged to discuss your employment, character and abilities. You should seek advice of counsel to determine if what is happening to you is unlawful, or the unfortunate result of a poor, but perfectly lawful, work place environment.
You need to talk with a skilled and experienced applicant's worker's comp attorney if you intend to pursue claims of work-related injury. A work comp attorney can explain to you the special issues that are raised by claims of work-related injury based solely on employer disciplinary or termination actions.
Your headline question, "what can I do," presumably to salvage your job: no one here can possibly have a grasp of the situation sufficient to advise you. What you describe is a very untenable situation, it goes without saying, and you cannot be rationally anticipating that your employer would "turn around" on the issue of your value as an employee based on your present claims of work-related injury.
So, it seems that you are hoping that your claims of injury will force your employer's hand and cause your employer to have no sound option but to retain you. Don't invest too much in the potential success of that strategy. Employers make very bad hostages and employment is an unpromising environment for anyone to try and play out that hand. Face it, every single day that you or any other employee reports to work, it is factually likely that the employer could find some non-prohibited wholly lawful basis in your performance for termination -- if the employer even had to state a basis and almost always they do not have to put forth a reason.
You need to achieve some real clarity about your objectives in this situation. Talk to a good work comp attorney before you proceed deeper into this territory.
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