This is not acceptable behavior of your employer. First, make sure what the law is, (so do your homework) contact Union, centre for discrimination/diversity/inclusion or equal in your country. (if exists) Ask for a informal meeting with your supervisor or a level up, explain what happend, and why their actions are discriminatory. You can always write a letter or mail, but don't expect a response. Face 2 face is best. Be prepared, documentation of your performance @ the job, knowing the law. Do not threaten or loose youre cool. Just a conversation of how you feel, and how this situation is dicriminating and they have no reason to fire you. Their argument is highly subjective, unmeasurable and wrong. (and against the law in your country) If the above does not work, it is time to be more assertive. I do not know how beacause I don't know the law in your country. But be carefull, too assertive might blow bridges. Best of luck ! Wish you all the best.