Here is a typical example of a situation where resignation would be premature and would make the potential wrongful termination and disability discrimination case more difficult to prove. Suppose you are off work on disability leave till April 30. On April 10, your employer tells you that you have to return to work by April 20 or you will be fired, and they don't care that your doctor's note instructs you to stay off till the end of the month. This is a situation where you are much better off letting the employer termination you then resigning before April 20, like some employee would choose to do. Here, resigning might completely eliminate a wrongful termination claim, since you actually haven't been terminated. Resigning may also create problems in obtaining unemployment benefits.
If you are thinking of resigning and taking legal action against your employer for discrimination, retaliation or wrongful termination, consult a knowledgeable employment attorney in your area before you actually resign. Your attorney may be able to help enhance your case or even prevent those mistakes that will turn a good case into a not-so-great case or no case at all.