Unite regional officer Tony Ellingford told Foodmanufacture.co.uk that the Union will serve notice on the company of a ballot for strike action this week.
Strike action, which may include an overtime ban and strike days, will start in about five weeks if members vote in favour.
Ellingford said: “The majority of our nearly 300 members at the three British Sugar plants are telling us that they are prepared to take industrial action, although the ballot has yet to get underway.”
The Union had been collating detailed data on names, addresses and job titles of its members at British Sugar in the last month as it prepares to ballot, he said.
Ellingford explained that precise details were required in case British Sugar tried to block strike action on legal technicalities, following challenges from employers to strikes at companies such as British Airways.
The Union’s members at plants Wissingham near King’s Lynn, Cantley near Great Yarmouth, Bury St Edmunds and Newark in Nottinghamshire have rejected a 3.5% pay offer from British Sugar.
Unite is demanding a pay rise in line with retail price inflation of 5% plus 0.5% for the year from April 2011.
Ellingford said: “British Sugar is a profit-making company, we would be a lot more understanding if it was making a loss. What you have with the economic downturn is a lot of profitable companies jumping on the bandwagon and taking the opportunity to plead hard times to reduce their wage bill.”
The Union was prepared to go to ACAS [the Advisory, Conciliation and Arbitration Service], he added.
There had been no disputes at British Sugar for 30 years, and it was “sad” that the situation could not be resolved, he said.
British Sugar said in a statement: “The pay offer of 3.5%, which was recommended for acceptance by the trade unions, remains open. British Sugar would welcome the opportunity to discuss acceptance of this final offer with Unite union officials. In the meantime, we await the outcome of the ballot by Unite Union members.”