Many employers assume that they can demote an employee as a disciplinary measure and are shocked to learn that doing so might constitute a constructive dismissal. In fact, it will be a constructive dismissal in most cases.
Demoting an employee and potentially lowering their pay is a decision that has implications for both the employee and the employer. These implications can range from hurt feelings, all the way to a wrongful dismissal claim.
Can an employer rely on information they acquire after termination to allege that there was just cause for dismissal? Yes. Can an employer dismiss an employee for cause because they secretly recorded interactions at work? Yes.