Thank you for trusting your question to JA today. I am a licensed attorney with over a decade of law practice and nearly 20 years of experience in the legal field. I’m happy to be of assistance.
In employment law, if you do not have a contract of employment that expressly states that you can only be terminated for cause, your employment is "at will." An at will employee can legally be terminated without cause. An at will employee can be terminated for a cause that isn't really valid. The employer doesn't have to provide proof or even state a coherent reason.
So unless you had an employment contract like I mentioned, you can't force them to give a reason for your termination. You can certainly file for unemployment and that would force the employer's hand, because they would have to either allow it or contest it, and then they would have to give a cause. You'd be able to fight that cause because you'd know what it was AND you'd be in a stronger position, because they refused to give you the cause when you were terminated and that will make it appear as though they are now fabricating or overstating a cause just to avoid the expense of unemployment.
Now, you also stated that you believe you were terminated based on the false statements of others. If you know who, you can sue them individually for defamation of character, with the damages being the loss of your job. They made false statements of facts about you to another party (your boss) which caused you harm. Knowing the exact accusations made against you is difficult though, but the former employer could be subpoenaed to give information on what exactly was said and by whom.
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