Up to 140 jobs will be lost at The Warehouse, as the country's biggest retailer restructures its store leadership.
The Warehouse said it was the first change of its kind in 15 years and would lead to job losses across its 92 stores.
Chief executive Pejman Okhovat said the changes would lead to increased staffing levels at peak times, better leadership support during trading hours, improved sick and holiday cover and better-defined career pathways for team members.
He said the company would make an effort to re-deploy as many team members as possible into vacant roles, but it was expected to be between 120 and 140 fewer full time equivalent roles.
The new structure should be in place early next month.
First Union said workers would have to re-apply for their jobs over the next few weeks, before finding out if they will actually be made redundant.
A union spokesperson, Kate Davis, said the consultation period was a sham and staff were confused about the changes.
"I spoke to one of the checkout supervisors today, she's been there 23 years and she said 'Look I'm just not qualified for the role that they would want me to apply for and I won't get it'," she said.
Ms Davis said The Warehouse did not have enough time to go through all the feedback about the changes.
In a statement, The Warehouse defended the way it had handled the restructure.
"We're confident that the process we undertook was transparent and fair for our team members.
"We've communicated carefully and clearly throughout and believe we've struck the right balance between considering feedback thoroughly, while also not leaving team members waiting for too long," the statement said.
The Red Sheds employ 7277 people around the country.