The retailer has announced changes to store operations and a shake up of roles.
Unite, Britain’s biggest trade union, released a statement expressing “severe disappointment” at the changes.
In the process of buying Home Retail Group for £1.4bn, Sainsbury’s said it hoped to redeploy affected staff.
“We currently employ 870 store trainers,” a spokesperson said. “We’re now creating around 280 learning and development manager positions and all affected colleagues will have the opportunity to apply for these more senior roles.”
Julia Long, Unite’s national officer for food and drink, said: “We are severely disappointed as Sainsbury’s seems to have deep pockets when it wants, as it has forked out to purchase the Home Retail Group. Unite will be giving our members maximum support at this difficult time.”