A union says it will "seek clarity" on the future of Colman's Mustard in Norwich this week - after Britvic confirmed it was closing its adjoining factory in the city.
The manufacturer of Robinsons and Fruit Shoot drinks co-owns the Carrow Works site with Unilever, which makes Colman's.
Yesterday (Friday), Britvic confirmed it would be moving its production out of Norfolk and over to its other factories in the UK. More than 200 people work for the company in Norwich.
Unite the Union described the decision as a "hammer blow" for workers and accused the company of trying to "bury bad news" by "sneaking out" the announcement in the lead up to Christmas.
When Britvic announced it was considering closing its half of the factory back in October, it prompted Unilever to admit it was also reviewing the future of its site - and the 200-year history of Colman's in Norwich.
It puts more than 100 other jobs at risk.
Unite said it understood Unilever was still carrying out its review - but pledged to find out more soon.
Norwich South MP Clive Lewis has been campaigning against the closure of both factories.
He called yesterday's announcement "a real kick in the teeth to the city of Norwich" - and claimed on Twitter workers had been told their jobs were going during Britvic's Christmas lunch.
Britvic's chief executive insisted the decision had not been "made lightly" and said it was a "sad and difficult time".
But he claimed the move would lead to productivity and efficiency savings, as well as environmental benefits.