A Māori mum misidentified as a trespassed "thief" at a Rotorua supermarket trialling facial recognition technology says she felt "racially discriminated" against and embarrassed during the "horrible" birthday incident.

The store is part of a six-month trial of facial recognition technology in 25 of Foodstuffs' North Island supermarkets, which is being monitored by the Privacy Commissioner.

The technology scans customers' faces and compares these images to those on the store's databases of known offenders or suspects.

She said on the evening of 2 April, her 47th birthday, she stopped in with her teenage son to buy chops to go with fried rice from a Chinese takeaway.

She said two male staff approached her in the meat section and one got "literally in [her] face" and loudly told her: "You have been trespassed and you need to go".

She said they insisted she leave, even when she offered photo identification.

Solomon said the "horrible" ordeal went on for about 10 minutes before she and her son left the store without the chops, and she broke down in tears in the carpark.

She said she felt helpless and the incident "ruined what was until then a wonderful birthday".

Consumer New Zealand's chief executive Jon Duffy said the use of this technology was "highly invasive" from a privacy perspective, "like using a sledgehammer to crack a nut".

"Many New Zealanders don't have a choice where they shop which means they may be forced to give up their data, whether they like it or not."