MCBD, which has handled the account for two years, has declined to repitch.
Kendall Gordon, Thomson's marketing and strategic development director, said: "We have been delighted with the advertising MCBD has created for us. Our decision was purely because we wanted to keep our options open."
He added a review of the media and digital account is likely to follow. The briefs are held by The Media Shop and Dare on a project basis.
The review follows the appointment of Thomson's new chief executive, Max Alexander, who joined in January.
Last month, Yell, a rival to Thomson in the directories market, kicked off a review of its £20 million creative account. MCBD has been invited to pitch alongside Mother, United London, VCCP, Leagas Delaney and Wieden & Kennedy.