Are you in US?

If so, start job search, now.

what your manager did is unreasonable. the fact that your manager usually has total discretion regarding how much you work and in what hours you work indicates that he/she is not satisfied with you. they are looking to get rid of you by making your life difficult, and it may get worse and worse. it's a sign that you should consider to move on.

it is considerably difficult under your circumstance and under the general economy. but in the end, it is better to find a way-out yourself rather than fight this thing through the legal system.

the bottom line is I don't think you have a claim under the US legal system.