Private prison operator Serco says a report into organised fighting at Mt Eden Corrections Facility includes anonymous, unverified allegations and it wants it to be rewritten.
Today, in the High Court at Wellington, the British-based company is seeking a judicial review of the investigation by the Chief Inspector of Prisons.
The chief inspector's report on Mt Eden prison was completed last year, but it has been held back because of Serco's legal challenge.
The company's lawyer, Hayden Wilson, told the court this morning that the investigation had departed from the terms of reference, contained errors of law, and had omitted relevant factors.
The company said: "Serco claims that by relying on anonymous claims and allegations, which have not been verified or corroborated, the report is a breach of natural justice."
It was seeking an order that before the report was released, it was revised to "provide a fair and accurate account of the situation at Mt Eden".
The High Court hearing is set down for two days.
Mr Wilson said the judicial review was not an attempt by Serco to avoid criticism, and the company accepted most of the recommendations in the report.
However, the inquiry had expanded from its initial focus on organised fighting into a wider investigation of Serco's management of the prison.
Justice Karen Clark said the terms of reference allowed the chief inspector to investigate beyond organised fighting into general prison safety.
Mr Wilson said Serco accepted this, but that did not excuse the "wide-ranging detours" taken by the chief inspector.
He said the chief inspector also failed to verify some allegations, despite their "sensational"nature. These claims had ended up in the draft report completed in September.
Mr Wilson said the investigators had breached natural justice by failing to provide information about adverse findings, which would have allowed the company to respond.
In particular, Serco wanted interview notes taken by the chief inspector's team and, in some cases, the identity of the people making allegations.
If Serco knew who was making the allegations it could have provided greater detail, and also possibly identified whether any problems were isolated to a single prison unit.
On the rare occasions when these details were provided, Serco was able to respond in detail and the report was amended.
