The Birds Eye frozen food factory in Grimsby, North East Lincolnshire, is to close with the loss of 600 jobs.
The decision follows a year-long review of operations in Grimsby, Hull and Lowestoft by parent group Unilever.
News that the Grimsby plant will close early next year was broken to staff at a meeting on Thursday morning.
The GMB’s Andy Worth said: “It is a disgraceful and ridiculous decision that will put the livelihoods of 600 people in Grimsby in serious jeopardy.”
James Hill, chairman of Unilever’s ice cream and frozen food division, told the BBC: “It is a very difficult day for everybody and emotions are understandably running high.
“I would just like to say what tremendous sympathy I have for the Grimsby workforce and express my commitment to do everything possible to mitigate the effects of the change.”
