Warner Bros' New Line unit is warning an Ombudsman's ruling that the Government needs to release Hobbit-related documents jeopardises future film-making in New Zealand.

The Ombudsman ordered the Government to release documents about the deal it struck to ensure the Hobbit movies were made in this country.

Radio New Zealand applied for the documents in November 2010 under the Official Information Act but ministers refused on the grounds they were commercially sensitive.

The broadcaster and NZ Council of Trade Unions president Helen Kelly appealed the decision and on Thursday Ombudsman David McGee ruled that 18 documents, including emails between Hobbit director Sir Peter Jackson and Government officials, must be released.

The Government secured the three movies by changing employment laws and beefing up the tax rebate sweetener for the productions.

Unions fought the law changes and the Labour Party accused the Government of chequebook legislation.

In his 29-page ruling McGee said the information in the documents didn't pose serious commercial risks.

But the ruling quoted New Line as saying some of the documents reflected the company's "negotiations and innermost thinking, including certain strategic decisions, legal and personal opinions, offers from third-party governments and other private information", The Hollywood Reporter said.

New Line warned: "If the Government is not willing to adequately protect this sensitive information from disclosure, this will operate as a major disincentive to motion picture studios as well as local and foreign talent - to utilise New Zealand as a location for future productions."

A studio spokesperson declined to comment.

Jackson's Wingnut Films was quoted in the ruling: "I can categorically assure you that if the above information was released and a similar situation occur in the future, neither myself nor Wingnut Films would be inclined to help the Government again with such a candid level of advice and opinion."

The ruling did not indicate whether "I" referred to Jackson.

The Ombudsman declined to order the release of a 2010 Crown Law opinion which formed the legal justification for the Government's decision to weigh in on the side of the studio and Jackson, and against the union, New Zealand Actors Equity, which was trying to organise local actors on The Hobbit.

Ministers must hand over the documents on or before March 1 unless the Cabinet overrules McGee by invoking a veto which was introduced in 1987 but has never been used.

The first film of the Hobbit trilogy, An Unexpected Journey, premiered in Wellington in November and was a huge financial success internationally.

Prime Minister John Key said production generated 3000 extra jobs and New Zealand gained priceless tourism publicity.