Supermarket giant Sainsbury's is creating a new management role for training staff which union leaders say could lead to the loss of hundreds of jobs.
Unite said it will campaign to reduce compulsory redundancies and redeploy staff.
Sainsbury's said in a statement: "We've introduced new learning and development programmes to ensure our colleagues can continue to deliver the very best service to our customers.
"Following this we're now creating a new management role that will provide enhanced training support across a number of stores. This position will replace the existing store trainer role.
"We're conducting a consultation process with all affected colleagues, who will have the opportunity to apply for the new, senior roles.
"We currently employ 870 store trainers. We're now creating around 280 new learning and development manager positions and all affected colleagues will have the opportunity to apply for these more senior roles. We will also look to redeploy affected colleagues where possible."
Unite national officer Julia Long said: "This is very bad news for those dedicated workers affected by the planned job losses and Unite will be giving our members maximum support at this difficult time.
"We are severely disappointed as Sainsbury's seems to have deep pockets when it wants as it has just forked out £1.4 billion to purchase the Home Retail Group.
"We appreciate that Sainsbury's has a good record of redeployment of staff in these situations and we will be exploring every avenue to ensure continuing employment for our members.
"We are now entering the 45-day consultation period and will be having meetings with management, including asking the company if it has done an equalities audit of those affected by today's announcement."