The employer may legally *ask* for it, just as any person could *ask* your lawyer to disclose what you and he discussed; however, the doctor's office should not provide it (and does not have to provide it) without your authorization (just like a lawyer could not discuss what you and he talked about without your permission). Note that if there is some issue about, say, injuries or absences, and you do not have an employment contract protecting you, your employer could ask you to get this from the doctor or authorize them to get it from the doctor, and very likely terminate you if you do not.