Fanta is talking to other Coca-Cola roster agencies about its advertising account, leaving the role of the incumbent, Nitro, in question.
Nitro has worked on the soft-drinks brand for the past five years. It picked up the £3 million business in 2000, when it was the independent Soul. Soul was fully acquired by Nitro, the network headed by Chris Clarke, in June this year.
Mother created the most recent advertising campaign for Fanta, in May this year. The £2 million project promoted the diet variant Fanta Z.
The Mother campaign marked the first step in a radical change in strategy, which involved Coca-Cola switching the lion's share of its advertising budget into its diet brands.
The Mother TV spot featured people swigging Fanta Light and then spitting it out. The idea was used to illustrate the point that the old diet Fanta tasted horrible, but that things had changed. It used the line: "Hello Fanta Z."
The spot was given a watershed restriction after 272 people complained the ad promoted bad manners and antisocial behaviour.
Viewers complained that the ad condoned spitting and that children were mimicking the ad.
The move leaves Nitro with Coca-Cola's Five Alive fruit juice business.
However, the account has been dormant over the past 12 months.
Cathryn Sleight, a brand director at Coca-Cola GB, said: "All of our roster agencies continue to play a valued role as part of the portfolio of creative agencies which work for The Coca-Cola Company.
"We are constantly reviewing best ways of working, in order to maximise our agencies' creative talents across our portfolio of brands, both from a UK and from a global perspective."
The most recent Coca-Cola pitch was concluded last month and resulted in Wieden & Kennedy Amsterdam picking up the "big idea" brief to promote the flagship Coke brand globally.
W&K will develop an overarching idea for the brand, which will then be adapted for local markets.
Also in October, W&K's Portland office walked off with the flagship $150 million Coca-Cola North American account. It swiped the account without a pitch from Berlin Cameron United.