Great question Newhoff.  This happens ALL of the time in our industry.  I see employers going beyond the list of references that are provided by contacting other folks that they know these people work with - fellow employees that the hiring manager may know, mutual clients that were discovered during the interview process, etc.  This certainly makes sense, as MOST of the time people put down references that are of course going to vouch for them, so hiring managers look for some inside information that is honest and not necessarily so biased.  This is how it always has been and this is how it always will be.  Even though most employers do not allow for their employees to give references, this rule usually never is followed.  So...make sure you work hard, you get the job done accurately and in a timely manner, make sure you treat your underlings, your peers, your supervisors and your clients with respect and professionalism, because you never know who is asking about you.

Our application has a signature block that includes the comments that you authorize us to check you out. It doesn't say, "by only the names/ #s you provide to us". We also allow candidates to tell us/ mark current ER for us NOT to call. If a recruiter or ER calls anyway, shame on them! That's a poor practice. They wouldn't survive on my HR team if they did that.