"Unprofessional" is too vague term. What exactly the employee has done so that you call him "unprofessional". Were there series of incidents?
By the way, what is your designation? Does this employee report to you? Is it that you are from HR and some unprofessional behaviour has come to your notice?
Have you given feedback to the employee? What is his response to your feedback? Was there no change in his behaviour?
Please elaborate your post further.
Dinesh V Divekar
22nd July 2014 From India, Bangalore