What should employees do when their supervisors are tribalistic at work? And adding monopolistic power to themselves?
You deal effectively with this by learning how to NOT act when you are a supervisor. You also learn how to deal with this by.... filling out job applications at competitors.
Consult with a lawyer if these are legal practices. If they're legal, you may think they're not fair but they're legal. So you have the right to leave at any time you want.