A group of heritage campaigners says Auckland Council members were misled by officials when they decided not to protect three partly demolished art deco houses.
The Art Deco Society's lawyer has told council that officials overstated the financial costs of a last-minute legal process.
The developer has agreed to halt demolition until mid-January while Mayor Len Brown seeks a compromise.
The society failed a fortnight ago to persuade councillors to to impose a protection order on the houses in the suburb of St Heliers.
Most of the councillors accepted advice from officers that the council would probably lose a subsequent court process and could face millions of dollars in costs.
The society has sent the council a legal opinion saying the financial risks are more likely to be tens of thousands of dollars.
The fate of the houses is still undecided.