The Unite union warned that the closure could also jeopardise production of Colman’s mustard, an iconic brand made at the shared site by Dutch-British transnational corporation Unilever.
Production of the Robinsons and Fruit Shoot brands will be transferred to east London, Leeds and Rugby, and the plant will close by late 2019.
Unite national officer Rhys McCarthy said: “This is very painful news for our members and their families at Britvic and we will be giving the maximum support to our members at what is a very difficult time in the days and weeks ahead.”
He said the closure “also has an impact on Unilever workers who share the same site.”
Mr McCarthy said that Unilever had announced a review of its operations in Norwich, where Colman’s mustard has been produced for more than 200 years.
The site employs about 60 workers who are members of Unite or fellow general union GMB.
Mr McCarthy pledged: “Unite will not only be seeking assurances but applying pressure with the support of the local community that the production and the much-needed jobs that are vital for the Norwich economy remain.
"Anything else won't cut the mustard.
“The whole of Norfolk needs to come together to fight for the future of Colman’s mustard that is so identified with the city of Norwich. Colman’s is in the DNA of the city.”