Employers may not ask job applicants about the existence, nature, or severity of a disability. Applicants may be asked about their ability to perform specific job functions. The ADA prohibits employers from asking questions that are likely to reveal the existence of a disability before making a job offer (i.e., the pre-offer period). This prohibition covers written questionnaires and inquiries made during interviews, as well as medical examinations. However, such questions and medical examinations are permitted after extending a job offer but before the individual begins work (i.e., the post-offer period).
A job offer may be conditioned on the results of a medical examination, but only if the examination is required for all entering employees in similar jobs. Medical examinations of employees must be job related and consistent with the employer's business needs. http://www.eeoc.gov/laws/practices/inquiries_medical.cfm
If you have a disability, you must also be qualified to perform the essential functions or duties of a job, with or without reasonable accommodation, in order to be protected from job discrimination by the ADA. This means two things. First, you must satisfy the employer's requirements for the job, such as education, employment experience, skills or licenses. Second, you must be able to perform the essential functions of the job with or without reasonable accommodation. Essential functions are the fundamental job duties that you must be able to perform on your own or with the help of a reasonable accommodation. The employer cannot refuse to hire you because of your disability if you can perform the essential functions of the job with an accommodation. An employer cannot refuse to hire you because your disability prevents you from performing duties that are not essential to the job. http://www.eeoc.gov/facts/ada18.html
An applicant with a disability, like all other applicants, must be able to meet the employer's requirements for the job, such as education, training, employment experience, skills, or licenses. http://www.eeoc.gov/facts/jobapplicant.html
Employers are required to provide reasonable accommodations during the application process. If the requested accommodation causes an undue hardship, the employer still would be required to provide another accommodation that does not. The ADA requires that employers give application tests in a format or manner that does not require use of your impaired skill, unless the test is designed to measure that skill. If your disability and need for accommodation are not obvious, the employer may ask you for reasonable documentation explaining the disability and why an accommodation is needed. An employer has to offer an accommodation that will meet your needs. If more than one accommodation meets your needs, then the employer may choose which one to provide. You cannot insist on a specific accommodation only because it is a personal preference. If the employer's proposal does not meet your needs, then you need to explain why (http://www.eeoc.gov/facts/jobapplicant.html#application).
An employer can ask all of the questions that are likely to reveal the existence of a disability, after it extends you a job offer as long as it asks the same questions of other applicants offered the same type of job.In other words, an employer cannot ask such questions only of those who have obvious disabilities. Similarly, an employer may require a medical examination after making a job offer as long as it requires the same medical examination of other applicants offered the same type of job (http://www.eeoc.gov/facts/jobapplicant.html#application)
If the employer believes an applicant with an obvious disability will need a reasonable accommodation to do the job, it may ask the applicant to describe or demonstrate how she would perform the job with or without reasonable accommodation (http://www.eeoc.gov/facts/jobapplicant.html#application)
Determining the best moment to tell a prospective employer about the need for reasonable accommodation on the job is a personal decision. Sometimes, applicants are not aware they may need a reasonable accommodation until they have more information about the job, its requirements, and the work environment. Some applicants choose to inform an employer during the application process after they better understand the job and its requirements. Others choose to wait until they have a job offer. http://www.eeoc.gov/facts/jobapplicant.html#application