Up to 45 staff at Woolworths supermarkets in Griffith and Leeton could be removed from their managerial positions under a new operating model.
The company said the restructure would create two new dedicated fresh food teams.
This means separate deli, butchery and seafood managers and other managers will be removed from their role and asked to re-apply for a non-managerial position, under plans for a single manager to oversee the combined teams.
According to Woolworths, the new model will give staff members more opportunity to build new skills and career paths, without reducing their head count.
But Retail and Fast Food Workers Union secretary Josh Cullinan said the positions of many of the 10,000 Woolworths managers nationwide would be made redundant.
"There is a lot of shock, a lot of people who are upset and there is a great deal of surprise, particularly for many who have worked with the company for decades," he said.
"We have made a series of demands to Woolworths to delay the implementation of the re-structure until they have properly consulted, to guarantee the take home pay of workers so there are no wage cuts, to guarantee ever worker who wants to stay with the company will be retained in a job and to enhance packages for those who are retrenched.
"Obviously the expectation for someone who has been a department manager for 20 years to take up a casual or part-time weekend job just won't happen."
The union estimates the model will affect between 10 and 15 managers in each store. There are two stores in Griffith and one in Leeton.
Woolworths Supermarkets managing director Claire Peters said the new operating model would create more customer facing leadership roles responding to feedback from customers they want to see more team members available to help on the shop floor.
"We understand the changes we're making to our store operating model may create uncertainty and stress for some of our team members. We're committed to working closely with impacted team members to identify potential redeployment opportunities in our business over the coming months," she said.
"Importantly, the changes will not lead to a new reduction in the number of team members we employ in our stores. However, we do understand the new opportunities in the revised structure may not appeal to everyone, and will make sure those team members are fully supported in their transition."