Part of Title I was found unconstitutional by the United States Supreme Court as it pertains to states in the case of Board of Trustees of the University of Alabama v. Garrett as violating the sovereign immunity rights of the several states as specified by the Eleventh Amendment to the United States Constitution. The Court determined that state employees cannot sue their employer for violating ADA rules. State employees can, however, file complaints at the Department of Justice or the Equal Employment Opportunity Commission, who can sue on their behalf.
If you have a disability and are qualified to do a job, the ADA protects you from job discrimination on the basis of your disability. Under the ADA, you have a disability if you have a physical or mental impairment that substantially limits a major life activity. The ADA also protects you if you have a history of such a disability, or if an employer believes that you have such a disability, even if you don't.
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. 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.