First Union regional organiser Kaye Hairfield said the ongoing process had been anxiety-inducing for workers who just wanted some security and stability in uncertain times.
The union said The Warehouse in Trafalgar Square currently had about 60 full-time equivalent staff.
"There are some people that haven't retained as many hours they need or prefer, just to try to maintain a living standard," Hairfield said.
"Some people are okay and have managed to lock in what their preference, others haven't been so lucky."
The Chronicle has approached the Warehouse Trafalgar Square and the head office for comment.
Last week The Warehouse posted a $44.5 million profit in the 2020 financial year.
The company, which operates The Warehouse, Warehouse Stationery, Noel Leeming, Torpedo7 and TheMarket.co.nz would have made a loss without the $67.7m it received in wage subsidies.
"We challenged them in the respect of fairness," Hairfield said. "The company took on board our views and they went back to the drawing board, but they have come back with still wanting to do a national rollout of restructuring and then we have just had to go through that process.
"Workers generally felt extremely frustrated that their whole livelihood and their incomes were turned upside down again just to accommodate the focus of the company."
With Christmas and summer around the corner, Hairfield said employees may have an opportunity to regain hours in the coming months.
"It may give workers an opportunity of picking up additional floating shifts. But for them, it's about locking in an income for stability," she said.
"It's all very well for any employer to say you have an opportunity to pick up additional hours, but for our members they want these hours to be permanent."