DFGW, Burkitt DDB and the incumbent, Beechwood, were involved earlier in the process, with the final shoot-out between St Luke's and Beechwood conducted last month. The review was handled by the AAR.
Waterstone's, the UK's biggest bookstore chain, has until now worked with agencies on a project basis. Beechwood handled the store's Christmas campaign. This used a pantomime theme to launch the retailer's three-for-two paperbacks promotion. It ran across TV, press and outdoor and used the line: "Make a wishlist."
The review is not thought to affect Waterstone's media agency, PHD.
Waterstone's has nearly 200 stores across the UK and Ireland and its flagship branch on Piccadilly in London is the biggest bookshop in Europe.
A Waterstone's spokeswoman denied a final decision had been made and said an announcement would be made by the end of July.