Thank you for the additional information. I am sorry to hear of your dilemma. I realize how frustrating this is for you and I hope to provide you information which is accurate and useful, even though it may not be the news you were hoping to get.
Unfortunately, as such, you serve at the whim of your employer. They can change your duties, compensation (going forward), schedule or even terminate for any reason or no reason at all.
The only exception is that any action taken against you may not be motivated by illegal discrimination (race, religion, disability, ethnicity, etc.) or sexual harassment.
If, upon further deliberation you think that may apply to your situation then you need to make a complaint to the EEOC as soon as possible.
Otherwise, without a claim, as described above, the courts view this as office politics and offer no judicial or administrative remedy. In other words, you would need to seek recourse within the HR department.