A person may be disabled if he or she has a physical or mental condition that substantially limits a major life activity (such as walking,
talking, seeing, hearing, or learning).
The law requires an employer to provide reasonable accommodation to an employee or job applicant with a disability, unless doing so would cause significant difficulty or expense for the employer . . . .
A reasonable accommodation is any change in the work environment (or in the way things are usually done) to help a person with a disability apply for a job, perform the duties of a job, or enjoy the benefits and privileges of employment.
An employer doesn't have to provide an accommodation if doing so would cause undue hardship to the employer.
Undue hardship means that the accommodation would be too difficult or too expensive to provide, in light of the employer's size, financial resources, and the needs of the business. An employer may not refuse to provide an accommodation just because it involves some cost. An employer does not have to provide the exact accommodation the employee or job applicant wants. If more than one accommodation works, the employer may choose which one to provide.
http://www.eeoc.gov/laws/types/disability.cfm