Is it legal to ask an employee about their health history?
If the employee is not doing his job, the behaviors should be assessed and the employee should be given a chance to remedy the problematic behavior(s). If you suspect any employees of having a health problem or disability that is affecting their ability to do the job, it would be advisable to deal with the observable behaviors that are affecting your perception of their competence in their role instead of delving into the employees' health history. If the employee volunteers information that he cannot do the job for medical reasons, ask for documentation from his physician regarding what job duties he can do, under what kind of duration, and so forth. Then, accommodate these restrictions if you can.