The Commerce Commission is this afternoon emphasising that Countdown suppliers can contact it in confidence.
"The Commission advises that anyone who has information relevant to the allegations can request that the Commission keep their identity and/or the information provided confidential," the regulator said in a statement this afternoon.
"The Commission will not disclose the identity and/or information unless consent is given or the Commission is required to by law. If confidentiality is a concern then it should be raised when first contact is made with the Commission."
Late yesterday, the regulator confirmed it is assessing alleged anti-competitive behaviour by Countdown toward its suppliers.
The assessment follows Labour MP Shane Jones phoning Commission chairman Mark Berry, then following up with a formal written complaint.
"Anyone who has relevant information is encouraged to contact us on 0800 943 600," the Commission statement says.
A spokesman for the regulator refused to tell NBR if any suppliers have come forward so far.