Workers at a major food plant in Bury St Edmunds have been told up to 66 jobs – just under a fifth of the workforce – are at risk.

All jobs at the plant, off Mildenhall Road, appeared to be secure after Premier Foods revealed plans in 2012 to sell its Branston Pickle operation to Japanese firm Mizkan.

But yesterday Mizkan, which also bought Premier Foods’ vinegar and sour pickles business, confirmed it will be making cuts.

Outgoing Bury St Edmunds MP David Ruffley described the announcement as a “tragedy” for local families and bad news for Bury’s job market.

A Mizkan spokeswoman said a maximum of 87 jobs were at risk across three UK sites – Middleton in Greater Manchester, Chiswick Park in London and Bury St Edmunds – with up to 66 earmarked to go at the Bury plant, which has about 350 employees.

She said it was not known which roles would be affected at this stage, but did say no positions would go before Christmas. The consultation period is 45 days.

Mizkan said in a statement: “Mizkan Euro is currently undergoing a business restructure. Challenging environmental conditions within the UK food market have meant that a streamlining of processes, and implementing cost reductions, at Mizkan sites has become essential.

“A maximum of 66 roles are affected at the Bury site. Employees have been informed of the potential redundancies. A period of formal consultation will follow.

“The restructure will not affect the organisation’s manufacture or distribution of any of its products, including all products within the Branston, Sarson’s, Haywards ranges.”

One worker described the promises which had been made about job security at the Bury plant as “fake”.

Mr Ruffley said: “This site has been an important food plant in different incarnations over the years. It has supplied important jobs in Bury St Edmunds and when Mizkan acquired the site from Premier there were undertakings given to protect jobs. That was two years ago and this latest news about [up to] 66 jobs going is not only disappointing it is very serious.”

He has written to the chief executive of Mizkan about the “extremely disappointing” news, asking them to explain the reason for this unexpected round of job cuts.

Shaun Graham, senior organiser for the region for the GMB union, said the union had helped to iron out issues between the workforce and the new employer so the cuts were disappointing.

“I thought we were making progress in the right direction and I’m saddened, very saddened actually, to hear this announcement. It’s a lot of people going from a production [team] that has somehow got to still get out all these products.”

Colin Knight, chairman of Bury’s Chamber of Commerce, said: “Any job loss at any business in the town is bad news. I’m sure they have come to that decision in trying to consider all the economic factors that come into it. I would hope they are going to maintain as many jobs as they possibly can.”