One source close to the IPA said: "There's a general sense that agencies are paying too much versus TV contractors for a service that is there to help the contractors. "
The IPA is the largest single shareholder of Barb, with TV companies then contributing according to their size and revenues.
Sources said talks could "take months", especially as Barb is still in talks with research companies about issuing its next contract.
Lynne Robinson, the IPA's head of research, said: "As part of the new Barb contract, we are looking at the scale and scope and how much a cost change may affect value."
Bjarne Thelin, the chief executive of Barb, said: "This is routine when you get to this stage of a contract."