The ADA, and its amendment the ADAAA, require an employer to provide an employee with a disability a reasonable accommodation which allows the employee to perform the essential functions of the job. However, not all employees are entitled to accommodations and not all sought after accommodations are reasonable. That a look at this Q and A on Avvo.com:
https://www.avvo.com/legal-answers/do-i-have-a-claim-against-my-employer-because-they-2983173.html?answered=true