Typically most employees are at-will, meaning that your employer can fire you for any reason or no reason at all. Thus, your employer is legally...

If you signed a non-compete agreement upon your hiring, the court usually holds those out to be valid as long as the non-compete does not last...

You may be able to sue your former supervisor, who cost you your new job, for defamation or tortious interference with a contract. For defamation...

If the company you work for is a private company then you likely do not have any legal recourse.