Walker handles the £5m First Choice media spend; MPG the £7m Thomson spend; and Universal McCann Manchester the spend for Thomson's direct brand Portland.
It is understood TUI is looking at the possibilities of putting everything into one agency and of keeping the Portland account separate.
The review is being handled by Tim Williamson, director of product and marketing at TUI Travel, who was a marketer at First Choice before the merger.
Williamson said that while the relationships with the agencies have been "excellent", the merger meant TUI has a need to consolidate its arrangements.
TUI today appointed Beattie McGuinness Bungay to handle its consolidated creative account. Creative duties had previously been split between BMB, which handled First Choice, and Krow, which handled Thomson.
This article was first published on brandrepublic.com