Creativebrief is helping to run the pitch, which is still in the pre-chemistry meeting stage.
Chiltern is looking for an agency to create a brand campaign that will differentiate the train company from its competitors, as well as help launch new services.
The incumbent agency, Connect Group, has been invited to re-pitch for the account.
MediaCom Birmingham is Chiltern Railways’ media agency and is unaffected by the review.
Chiltern Railways uses two straplines, "If you think our way, travel our way" and "Nice and fast".
Previous TV campaigns have focused on the comfort in which Chiltern customers travel, while press and outdoor campaigns promoting its Birmingham-to-London service have attacked rival business Virgin Trains.
Chiltern Railways is owned by Deutsche Bahn and is part of Arriva, which runs Deutsche Bahn’s services outside Germany.