Fonterra's new light-proof bottles are being blamed by consumers for milk curdling before its use-by date.
Dot Larsen contacted the Waikato Times after finding that all four bottles of Anchor Mega Milk she had bought from Clarence St Pak 'n Save were curdled when she opened them.
Several people who read her letter then contacted the Times to say they had experienced the same thing.
All confirmed their milk was kept chilled, as did the store from which Ms Larsen bought her milk.
Ms Larsen said she did not usually buy the new light-proof bottles as she preferred being able to see how much milk was left in a bottle.
However, they were the only option at the Pak 'n Save, so she purchased four bottles of Anchor Mega Milk on July 14, with a use-by date of July 20.
She then drove straight home, and put three of the bottles in the freezer. The remaining bottle went into the fridge.
"We opened it the next day and it was curdled," she said.
Ms Larsen defrosted the other three bottles and found they were all curdled too.
"It was quite unusual, not what you would expect over a period of time. It looked like it was sort of being created by something interacting with the milk."
She rang Fonterra to alert them to the problem, and said the woman's response "rang alarm bells straight away".
"She didn't want to discuss things with me . . . she basically threw it back to Pak 'n Save."
Her partner then returned the milk to Pak 'n Save, where all four bottles were replaced.
Clarence St Pak 'n Save store owner Tony Rider confirmed that four customers had recently returned two-litre bottles of Anchor Mega Milk, although he said there may be more who had not bothered to bring it to the store's attention. He said checks of the milk fridge had been undertaken as a result of the complaints.
"Because we are in the middle of an upgrade, we have the refrigeration guys out here all the time and they have confirmed there were no problems."
He said it was unfair for Fonterra to point the finger at retailers since the company "brings it right in and puts it away". "The responsibility has got to go back to them."
General manager of retail for Foodstuffs, which owns the Pak 'n Save brand, confirmed the company has a strict policy when dealing with refrigerated items.
Rob Chemaly said he was "very comfortable that . . . all our chilled products are delivered and refrigerated immediately on delivery".
Anchor Group marketing manager Craig Irwin said the company had received several calls from customers about curdling.
"We've recently had a slight increase in calls from consumers with similar experiences. We appreciate that Dot is not in this camp, but some of the people who are calling our Customer Service team have misunderstood that the new Anchor Light Proof bottle will enable them to leave their milk out of the fridge for longer.
"For consumers and retailers alike, the optimum temperature for storing milk is 4 degrees Celsius."