I think you want to bring this case under Texas state law first. Federal law permits mandated OT as long as they pay you for it. Texas law restricts mandatory OT for certain areas of employment (I don't have that information in front of me).
As for termination, employers are allowed to fire employees as long as it is not an illegal reason. The list of illegal reasons are small: discrimination, retaliation, requiring employees to perform illegal actions, family and medical Leave, contract violations, and/or violation of the company's own termination procedures.
I am not a lawyer. Please speak with an employment attorney for legal advice.
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