Auckland Transport is making direct approaches to about 400 parties who own the 280 properties affected by its $2.86 billion, 3.5km, mainly underground city rail link.
Dr Stephen Rainbow, the manager of Auckland Transport's key relationships unit, said all property owners were being approached directly, either in person or by mail.
But he refused to give addresses until plans were much further advanced.
"We've sent out 400 letters and there's about 200 properties but some are unit titles. It's mainly commercial premises and at the Mt Eden end we have some residential complexes and even family homes which are potentially impacted and obviously they are highly sensitive and we're putting a lot of effort into that," he said.
"We're taking our time to approach most of the affected people personally so it [publication of a list] won't be helpful until all the people have been talked to."
Many of the properties earmarked for purchase are understood to be around the Flower St area of Mt Eden but Dr Rainbow said his organisation would not need to buy all 280 places and only a "relatively small" number would be purchased.
"This is about people who are potentially impacted, even if we're digging under their property. If you own a property in New Zealand, you own it right through to the centre of the earth, which is what I've heard in presentations from one of the technical people who would know."
Properties needing to be bought included those where the site was required for construction, he said.
"The reason to talk now is that we don't want to get into a situation of compulsory acquisition but we want to find out what people's plans are first. We can used compulsory acquisition as a last resort."
Discussions were being held with Westfield (NZ) over buying its Downtown mall.
On July 3, Auckland Transport released a detailed report about its plans for the 280 properties and how surface land would be required for station access where tunnels come to the surface to join the western line. Surface land would also be needed for work sites.
"Subsurface land [would be] required where tunnels and stations pass below properties," Auckland Transport said. "Subsurface numbers include 12 body corporates with multiple owners."
But no heritage or character buildings were needed, it added.
Planning and property issues are set down for the next three years, construction of the loop for five and a target opening date given of 2020-21.
Auckland Transport says the plan unlocks an Auckland-wide network capacity and allows more direct city centre access.
Is your property affected by the rail loop? Email email@example.com