Jobs could be on the line for dozens of Warehouse employees across the country.
The store asked staff for feedback on proposed changes on Thursday, which FIRST Union says could include 180 job losses across 92 stores.
FIRST organiser Kate Davis told Newshub some of those people have held their jobs for up to 25 years.
"The people that are being made redundant are the supervisors and team leaders - the people who thought they had a career in retail. I've had people in tears calling me, not knowing what's going on."
A Warehouse spokesperson said it was only a proposal at this stage and nothing has been confirmed, and wouldn't comment further.
Ms Davis said The Warehouse appears to be trading in "Kiwi values" for "Walmart morals".
"They've had nothing to do with Kiwi values, and it's the very workers which the company's success was built on - which is even more disturbing and distressing."
Walmart is a large US retail chain which has been criticised for years for its alleged low pay, anti-union activities and devastating effects on smaller, local retailers.
Ms Davis said many executives at the company are now on over $1 million a year, while floor staff are having their hours cut to make way for students earning NCQA credits instead of money.
"It's a slash-and-burn team of high-paid US executives brought in to undermine and destroy the security of work for New Zealand workers."
Ms Davis says the 10-day deadline for feedback is not long enough.
"We have lobbied and asked the company to reconsider the strict timeline they've offered, so people can offer genuine feedback and let the company know how they really feel."