At least two regional councils are refusing to issue lists they hold of sites potentially contaminated with toxic chemicals.
There is growing pressure on all councils to publish the information after the Ombudsman ruled the Hawke's Bay Regional Council had to do so.
Five of the 17 regional councils, including Hawke's Bay, have issued lists and at least two others say they will make theirs public later on Monday.
But Tasman District Mayor Richard Kempthorne says its list contains first-hand information provided by farmers and revealing it would break their trust.
Mr Kempthorne says the need to protect their confidentiality overrides the public's interest.
Canterbury Regional Council says it will release its list only if journalists pay a fee and sign a memorandum of understanding.
The Green Party says the councils are being irresponsible. MP Catherine Delahunty says she is drawing up a private member's bill to force all sites into the open.
List contents
The lists contain the location of thousands of sites where toxic chemicals were used in the past and were initially drawn up in the 1990s, but many landowners have never been told.
Hawke's Bay Regional Council says its biggest problem is the former landfill site at Onekawa park.
Chairperson Alan Dick says the council has whittled the number of houses likely to be sitting on the site to 100, and will now drill down into the site to check nothing is leaking.
Last week, the Northland, Bay of Plenty and Manawatu-Wanganui councils revealed they know of a total of 88 sites with confirmed contamination. At least another 1000 sites are still to be investigated.
