Bogus claims
Unfortunately, you do not have a right to find out who made the claims. Most people are employees at will and have no employment contracts or union contracts that protect them. That means that a boss can fire them at will for any legal reason other than discrimination on the basis of such things such as race, color, creed, etc. or no reason at all. If there is an employment contract, or a union, that's different.
If you do somehow find out who made the claims, then if yo can prove they did it, you could sue them for defamation.