Depends on the employer...as an example, if he's post office, he's broken federal law. If he has a union, the shop steward needs to be contacted. If not,
Your friend needs to have the supervisor state in writing what specific condition of employment he has violated. Is it published in the personnel handbook? When did it take effect? When was training conducted?
If he doesn't want to alert the boss, he might be able to make inquiries through the HR office.
This isn't legal advice.