29 C.F.R. § 1630.13 : Labor — REGULATIONS RELATING TO LABOR — EQUAL EMPLOYMENT OPPORTUNITY COMMISSION — REGULATIONS TO IMPLEMENT THE EQUAL EMPLOYMENT PROVISIONS OF THE AMERICANS WITH DISABILITIES ACT — Prohibited medical examinations and inquiries

(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.
(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.

29 C.F.R. §1630.13