Kate Davis, First Union national co-ordinator for The Warehouse, said the union was eager to know how many fulltime equivalent roles were at risk at each store.
"We have been asking for a spreadsheet but we have not been given it.
"If jobs are lost in Rotorua, unless they go to Taupō, there's not a lot of options," Davis said.
"We believe this is going to hurt the regions more than anywhere else."
Davis said she had been inundated with calls and messages since the announcement, including from Rotorua staff.
"People are horrified. These are stable workers who have given 10, 15, 20 years of their lives, that are now threatened with losing their livelihood."
Staff have been given until Sundayto provide feedback on the proposal and a decision will be made on July 15.
First Union is pushing for a longer consultation period.
Davis said she believed The Warehouse and Kmart were both at risk with the arrival of Amazon in Australia later this year.
"I believe that The Warehouse in its current form is struggling against the idea of Amazon and looking at ways to up its game," she said.
"It's a concern for Kmart too but they've been able to mitigate it."
Foodstuffs chief executive Chris Quin confirmed this week consultation had taken place and the Rotorua centre would close. Operations based at the site will move to a new centre in Auckland.
Quin said the initial announcement of 51 affected jobs may change.
"As the projected closure date is some time off (2020) that may change as team members explore other opportunities in the interim."
He said staff had a positive attitude during the consultation process.
"One thing that has really come through was how important the Rotorua team's family culture is to them and how they are looking out for each other.
"They've kept doing a fantastic job for our stores. This is a credit to the team's culture and they can be really proud of how they've handled this challenging news."
First Union spokesman Phil Graham said a number of people had left already because they wanted to secure employment.