It depends. You cannot be required by an employer to take a medical examination before you are offered a job. Following a job offer an employer can condition the job offer on your passing a required medical examination. This can only be done if all entering employees for that job category have to take the examination and the exam is job-related and consistent with the employer's business needs. (You cannot be singled out for an exam merely because you have, or your employer believes you have, a disability.) However, an employer cannot reject you because of information about your disability revealed by the medical examination, unless the reasons for rejection are job-related and necessary for the conduct of the employer's business. The employer cannot refuse to hire you because of your disability if you can perform the essential functions of the job with an accommodation.
Once you have been hired and started work, your employer cannot require that you take a medical examination or ask questions about your disability unless they are related to your job and necessary for the conduct of your employer's business. However, your employer may conduct voluntary medical examinations that are part of an employee health program and may provide medical information required by State workers' compensation laws to the agencies that administer such laws.
The results of all medical examinations must be kept confidential and maintained in separate medical files.