So here is a question that would be left to an employment lawyer but I'm going to through it out in response to what you have said: Assuming this is in the US,

So here is a question that would be left to an employment lawyer but I'm going to through it out in response to what you have said: Assuming this is in the US, would the employee's actions fall under the familial status protected class? If so, it would be illegal to fire the employee.