Public relations - book - was created in 1945.
Kyodo Public Relations was created in 1964.
ID public relations was created in 1993.
Public Relations Review was created in 1975.
Public Relations Journal was created in 1945.
Pierce Mattie Public Relations was created in 2001.
Chartered Institute of Public Relations was created in 1948.
Journal of Public Relations Research was created in 1989.
Guild of Public Relations Practitioners was created in 2000.
Asia Pacific Public Relations Journal was created in 1999.
Public Relations - Arrested Development - was created on 2004-01-25.
Public Relations - Mad Men - was created on 2010-07-25.
I think you mean to ask "what is the difference between public relations and employee relations?" In essence, there is not a difference. Employee relations is a specialty, a niche within public relations.