Be sure to read up on HIPAA law - there is no requirement for the note to reveal why your being treated (that's between you and your doctor, the confidentiality is protected by federal law).

If pressed by management, "I've been treated for a medical condition that precluded me from operating under Part 67, I am now fit to fly"

The Dr. note need only say that the employee was seen by a doctor.

CBA represented employees should talk to the legal dept. about any local requirements, but the take away is that an employer cannot ask you details of your HIPAA covered medical treatment.