The New Zealand Rugby Union is on a witch-hunt to smoke out the referee who analysed the World Cup quarter-final for the Herald.

High-performance refereeing manager Keith Lawrence has written to all 25 of his squad saying they should own up immediately or face the consequences of contributing to the "Refereeing the ref" article in Thursday's sports section.

The referee asked not to be identified because he was fearful of censure from the NZRU.

He gave English referee Wayne Barnes a 7/10 mark for the way he controlled the match - won 20-18 by France - identified some missed decisions, and said he would have sent two more All Blacks off.

In an email to referees on Friday, Mr Lawrence says: "I have a number of concerns about the appearance of such an article, as should each of you."

He does not detail what his concerns are, but says: "I can assure you all that now is the best time to own up."

All 25 of NZ's national referees are on the list, ranging from Steve Walsh, in charge of today's South-Africa-Argentina semifinal, to Ben Skeen, who controlled Saturday's game between Mid-Canterbury and Wanganui in the Meads Cup Heartland Championship.

"Your honesty in owning up will be a very significant mitigating factor in any decisions made about the article," Mr Lawrence tells them.

"Equally, if you do not own up and we subsequently discover who it is, the fact of not owning up will also be taken into account," he said.

"You owe it to your colleagues and the New Zealand Rugby Union to do the right thing."

Mr Lawrence gives the referees a list of questions and tells them to respond to him by email immediately.

He demands not only that the referee come forward, but that anyone who knows who it was to dob him in.

Referees contacted last night would not comment about the un-named referee who spoke to the Herald or about the email they had been sent, because they feared NZRU retribution.

They said they did not have the authority to speak, and directed all inquiries to the NZRU.

Keith Lawrence did not respond to Herald calls yesterday.

The union's professional rugby manager Neil Sorensen, said: "We are disappointed that a referee has chosen to publicly but anonymously comment on another referee's performance."