Even if the problems you are having at work do not rise to the level of illegal discrimination or retaliation, you will help yourself greatly by documenting the treatment you perceive to be unfair. Print out emails, save voicemail messages, and start a diary describing the actions your employer is taking against you. You can use these materials as ammunition in any severance negotiation you may have if you decide to leave your job or if you are fired.
Define Your Goals and Examine Your Options
After you have documented the treatment you perceive to be unfair, seek out a reputable and experienced employment attorney for a consultation. A knowledgeable lawyer can help you define your goals and give you different options and strategies for reaching them. You may want to preserve your employment for as long as possible. You may decide that it's time to move on. Whatever your goals may be, you should make a fully informed decision before you act.
Report the Unfair Treatment to Human Resources
If you plan to maintain your employment for a period of time, your lawyer may advise you to report the unfair treatment to your employer's Human Resources Department. This step makes your complaint "formal" and may have the effect of putting you into the whistleblower category. As a whistleblower, you have the same rights as victims of discrimination. Employers are generally afraid to fire or discipline legitimate whistleblowers. Your employer might also take steps to address the unfair treatment, but don't hold your breath.
If you plan on seeking separation pay and moving on to the next opportunity, you may want to have an initial "off the record" conversation with HR about your decision. Due to the sensitive nature of this discussion, you may want your attorney to handle it. In my experience, these kind of frank communications are generally well-received by employers looking to make a personnel change.
Execute the Plan
Whether you use your attorney's help or go solo, execute the plan that will best achieve your goals. If you plan on leaving or are terminated, formalize the severance negotiations in writing and get yourself the best package you can. If you plan on preserving your employment, continue to meet or exceed your employer's expectations and, at the same time, keep documenting any unfair treatment.