what can be done about a boss calling you a lier about an incident that you told the honest to god truth about

I have a family member that had put in a request for a shift change which he is entitled to due to seniority. But was denied in a letter from his superior stating that he is not eligable due to the fact that he had lied about an incident reguarding parts that was shipped. He had been questioned about the incident, told truthfuly what he knew about it as well as several other ppl. He was not responcible for what happened. This was approxamitly 4 months ago. Now he receives a letter stating that he will not be getting any libertys because he is a lier and should have been terminated. Is there anything he can do about this ??