Jerry can ask Peter why his performance has declined and may explore ways to ensure that mail is not misdirected. However, Jerry may not ask Peter questions about his intellectual disability unless there is objective evidence that Peter’s poor performance is related to his disability.
Generally, an employer may ask disability-related questions or require an employee to have a medical examination when it knows about a particular employee's medical condition, has observed performance problems, and reasonably believes that the problems are related to a medical condition. At other times, an employer may ask for medical information when it has received reliable information from someone else (for example, a family member or coworker) indicating that the employee may have a medical condition that is causing performance problems. Often, however, poor job performance is unrelated to a medical condition and generally should be handled in accordance with an employer's existing policies concerning performance.
Source: EEOC Guidance “Revised Questions and Answers about Persons with Intellectual Disabilities in the Workplace and the Americans with Disabilities Act,” reported in Employment Practices Guide ¶5374.