29 CFR §1630.13

1. (a)Pre-employment examination or inquiry. Except as permitted by § 1630.14, it is unlawful for a covered entity to conduct a medical examination of an applicant or to make inquiries as to whether an applicant is an individual with a disability or as to the nature or severity of such disability.
2. (b)Examination or inquiry of employees. Except as permitted by § 1630.14, it is unlawful for a covered entity to require a medical examination of an employee or to make inquiries as to whether an employee is an individual with a disability or as to the nature or severity of such disability.