British Sugar has announced plans to close two processing factories in Yorkshire and the West Midlands.
Two plants are set to close but four others should gain more work
The firm is to shut beet sugar sites at Allscott, Shropshire, and in York which together employ more than 200 people.
British Sugar said it would centralise work at four sites: Cantley and Wissington in Norfolk, Bury St Edmunds in Suffolk and Newark, Nottinghamshire.
But the National Farmers' Union (NFU) said the decision was a "kick in the teeth" to farmers.
It said that members faced losing contracts to supply British Sugar.
The NFU has pledged to negotiate the "best possible compensation package" from the sugar firm's owner Associated British Foods.
Four sites benefit
A union spokesman said: "The timing is a bolt from the blue.
"Sugar beet is the most profitable of the mainstream arable products and whatever farmers do instead is not going to return as much as sugar."
British Sugar said it planned to buy the 83,000 tonnes of additional sugar quota available in the UK following a reform of the EU sugar regime and expected to increase production at its four remaining sites.
The two threatened sites are likely to close at the end of next year. The Allscott factory was built in 1927, one year after the York site opened.
'Changes are difficult'
A spokesman for the company said the Allscott factory lacked scale for it to be run economically.
He said closing the York site reflected the poorer crop yields in northern England and falling sugar beet prices.
British Sugar provides about half of the UK's sugar requirement.
Chief Executive Officer Mark Carr said: "While changes like this are difficult, they are necessary if we are to ensure the long term sustainability of this industry in the UK.
"Our main priority now is to understand the individual needs of the people involved. Every effort will be made to identify alternative opportunities for those who may be affected by the planned closures."