The Commerce Commission has confirmed it will formally investigate allegations of anti-competitive behavior towards suppliers by Countdown and assured anonymity for those who require it.
In a statement, the Commission said its investigation was expected to take some months and it would be seeking a wide range of information from groups in all areas of the supermarket sector.
The inquiry appears to be limited to Countdown. The Commission has urged anyone with relevant information to contact it and undertaken to give anonymity to those who request it unless consent is given to disclose it or they are required to do so by law.
"If confidentiality is a concern then it should be raised when first contact is made with the Commission."
It has been considering the investigation since Labour MP Shane Jones lodged a complaint a week ago and used Parliamentary privilege to allege Countdown was forcing some suppliers to make retrospective payments to boost profit margins.
Mr Jones met with the Commerce Commission this afternoon and took in emails and other information he has relating to his allegations.
He defended his decision to raise it under the protection of Parliamentary privilege, but conceded he may have used some hyperbole to make his point.
He said he had heard that some staff at Countdown had been verbally abused by customers, which he regretted happening.
A spokesperson for Progressive Enterprise said "we'll fully cooperate with the investigation and we believe it's important now to let the process take its course."