Bartle Bogle Hegarty London has ended its relationship with the company that owns the J2O and Robinsons brands as it will not be repitching for the account.
Iris and 101 London also work on the account.
Britvic is planning to form a roster of two "frontline" agencies, one to lead adult brands and the other to focus on kids and family brands.
Matthew Barwell, chief marketing officer at Britvic, said: "We have had a long and fruitful relationship with BBH which has resulted in some of our most iconic work over the years, and whilst 101 and Iris are more recent partners they have also played a key role in providing strong creative stewardship to our stable of brands.
"As our market dynamics continue to shift, and as we grow internationally we feel the time is right to ensure that we have the right strategic partners in place to take us into the next phase of our business and to ensure we continue to deliver brilliant creative work."
The brand has enlisted the help of Creativebrief for the pitch, and expects to make a decision in July.
Ben Fennell, chief executive of BBH London, said: "We are proud of the work we've produced for Britvic over the years, however now is the right time for both parties to move on, so we will not be re-pitching."