Shock Jock Howard Stern took an unexpected day off from his radio show last week which prompted a firestorm of speculation on social media as to the underlying reason for his absence. Although Stern’s absence was initially attributed to a “personal day,” many fans speculated that Stern’s sick father was the real reason he missed work.

To quell the speculation, workaholic Stern revealed to listeners that he took a rare day off because he was, in fact, sick and his voice was not strong enough to do his radio show. Even after Stern’s announcement, however, some fans continued to sense a conspiracy and wanted more details, with one fan questioning, “If [Stern] taking a sick day is no big deal, why keep it a secret?”

Obviously irritated by the intrusion into his personal life, Stern asked, “Why was it such a big deal that I took a f**king day off?”

This incident brings up an important lesson for employers who may be speculating about the real reason an employee called in sick from work. Generally, the Americans with Disabilities Act (ADA) prohibits employers from asking whether an employee is an individual with a disability or about the nature or severity of a disability, unless the questions are job-related and consistent with business necessity.

According to the Equal Employment Opportunity Commission and some courts, asking an employee to explain the underlying reason for a sick day may violate the ADA. Thus, employers should refrain from asking intrusive questions that tend to reveal information regarding an actual or perceived disability.

Also, if your business has a sick leave policy that requires employees to provide a doctor’s note, you can steer clear of making an unlawful medical inquiry under the ADA by clarifying that the doctor’s note need only state: (1) the date on which the employee was seen; (2) that the absence from work was medically necessary; and (3) the date on which the employee will be able to return to work.

Lastly, you should train supervisors and HR personnel not to pry into the underlying reason for an employee’s use of sick leave unless the questions are indeed job-related and consistent with business necessity.