Thank you for the additional information. I am sorry to hear of your son's 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.
Without a written employment contract requiring cause for termination, your son is, in all likelihood, an at-will employee. As such, he serves at the whim of his employer. They can change his duties, compensation, schedule or even terminate for any reason or no reason at all.
The only exception is that any action taken against him may not be motivated by illegal discrimination (race, religion, disability, ethnicity, etc.) or sexual harassment.
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.
I am sorry. I wish I could tell you otherwise, but I do not want him spinning his wheels with this.
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