Bus. Eng: Whistle Blowing

  

a whistleblower
a tattletale
a rat
a snitch

to blow the whistle on s.o.
to tell on s.o
to rat s.o out
to rat on s.o

 http://idioms.thefreedictionary.com/blow+the+whistle
 http://www.usingenglish.com/reference/idioms/blow+the+whistle.html