Legal Question in Discrimination Law in Illinois

Your question concerns a change in conditions of employment. But in your case you are the one seeking to change a condition of employment. Your employer has come to expect you to report for work in your uniform and you have done so. It's my opinion only, that without your employer's permission to wear the hijab, you could face a disciplinary action and the employer would not be in violation of federal or state law. So if you have a sincere belief that you must wear the hijab, then make a written proposal to your employer including a photograph of how you would appear wearing the garment. If your employer approves of the change, no problem.