The Ministry for Primary Industries said yesterday it was investigating the matter.
Woolworths New Zealand acknowledged "increased pest activity" at Dunedin South Countdown, at 323 Andersons Bay Rd, near Hillside Rd, but said a comprehensive management plan was in place.
A store employee, who spoke to the Otago Daily Times yesterday on the condition of anonymity, said "one or two" rats were first detected inside the store in October.
Since then, they had multiplied and they said the supermarket was now "infested".
A pest control service was brought into the supermarket, but aside from an incidents register being filled out — where employees logged reports of the rodents — little had been done until poisoning began recently, the employee said.
The employee said droppings and urine had been evident for some time, but the rats were now increasingly visible and had been seen in the store during business hours.
"We’re selling food to the public that rats have been running over," the employee said.
"It’s a bloody disgrace. There are rats in the aisles. This is the 21st century, not Captain bloody Cook days."
Another employee, speaking on the condition of anonymity, said the pest control provider made recommendations that were ignored because they could have disrupted operations.
The "first book" of staff-reported rat activity would have had more than 100 incidents in it, they said.
The employee said droppings, urine, chewed products, and direct sightings of rats had all been reported.
Staff would work throughout the day and by the day’s end find fresh droppings in previously clean areas.
Over the past month, staff had started to find dead rats, including underneath the children's’s free fruit basket.
"It’s really bad and it’s kind of upsetting that nothing really has been done," the employee said.
A Woolworths New Zealand spokesman said staff claims that 17 dead rats had been found yesterday were "completely untrue".
"Food safety is our absolute priority and while we can confirm that our Dunedin South store has recently seen increased pest activity, we have a comprehensive pest management plan in place to deal with this.
"Using our specialist pest control contractor we are confident that the measures we are taking are effective."
To ensure the store was safe for both customers and staff there was increased routine cleaning, as well as additional deep cleaning.
There were also additional bait stations in place and the pest control contractor was making daily visits.
Staff were encouraged to report any pest activity or signs of it so the company could adjust its pest plan as required, the spokesman said.
New Zealand Food Safety deputy director-general Vincent Arbuckle said the ministry had received complaints about the matter and was investigating.
Food businesses were required to ensure the food they sold was safe and suitable for customers’ consumption.
"This includes pest management requirements," he said.
"As part of this process, food businesses are registered and regularly checked by an independent verifier.
"The verifier will check there are systems in place to ensure pests cannot enter food businesses and the pests are managed if they manage to do so."
As with all complaints, investigators would work with the business to determine the problem and seek a solution, Mr Arbuckle said.
If the food business did not put in place necessary corrective actions, there were enforcement tools available to correct the situation, he said.
First Union organiser Angus Wilson yesterday said he was aware of staff concerns about rats at the store.
He said the union had been in contact with Countdown.
