Some fund managers say they would like to see the full engineer's report on the state of Mighty River Power's power stations, because they have concerns about the company's insurance position in the event of a damaging earthquake.
The Mighty River Power share offer began on 15 April with the Government intending to sell 49% of the state-owned company. It is the first of three planned for partial privatisation.
Mighty River has given a summary of the Beca Carter Hollings and Ferner report in its prospectus, but is refusing to release the full report, saying it contains commercially sensitive details.
However, the summary letter says there are "certain elements" of its report which "may be relevant to a more detailed understanding of the Beca work and findings."
The summary letter, which is generally reassuring about the state of the company's power stations, is hedged with qualifications such as the generation system overall "appears to be generally in a good state of a repair" given its age and environmental factors.
The letter also says that "no statement in this letter should be construed as a statement of fact by Beca."