A Hawke's Bay man was shocked to find what he says were four pieces of glass in a slice of Value bread he bought from a local New World.
Foodstuffs says it takes food safety concerns seriously and is investigating what appears to be an "isolated incident".
Derek Timu and his family bought two loaves from Flaxmere New World on Sunday and were halfway through the second one when Timu discovered something untoward.
"I bit into the bread and I felt like a chunk of it in my teeth. I pulled it out and it was a clear piece of glass. I was like 'woah'," he said.
Timu said the glass was small in size, about "half the size of a piece of road bitumen", and impossible to see once he'd covered the slice with butter.
He said he was going to shrug it off and continue eating the bread, but decided to break apart the slice just in case.
It was then he found three more shards of glass, he said.
"They were very small, but they were enough that you knew exactly what they were," he said.
Timu contacted Foodstuffs and Flaxmere New World's owners had apologised to him, he said.
Foodstuffs spokeswoman Antoinette Laird said the bread would be sent to an independent lab for testing.
"Once this process has happened we will be in a position to confirm if the offending particles are in fact glass, and if so what type of glass.
"Fortunately, we have had no other reports of issues from customers so this appears to be an isolated incident – but we would encourage any customer who has a concern to reach out to our customer services team on 0800 245 114, who are more than happy to assist."
A second complaint from the same batch would trigger a product recall, the spokeswoman said.