Ogilvy Thailand chairman Alan Couldrey confirmed the news, describing the decision of an unnamed Ogilvy staffer to handle a project for Pepsi as "unfortunate".
Couldrey said: "It was something that shouldn't have happened. However, we (Ogilvy) still have Fanta (a Coca-Cola brand), and we're confident we can keep that relationship healthy."
The client is now believed to be in discussions with Coke roster agency McCann Erickson.