The Property Council plans to join the legal fight against an appeal of part of Auckland's Unitary Plan.
The Character Coalition and another lobby group, Auckland 2040, want a judicial review of the higher-density housing zones outlined in the plan, arguing some homeowners did not get a chance to make submissions.
The Auckland Council has said any new construction of townhouses and apartments in rezoned areas could be delayed significantly by the court action.
The Property Council's Auckland branch president, Phil Eaton, said the appeal came across as sour grapes.
He said the council, which represents commercial, industrial and retail property interests, had applied to join the proceedings in the High Court.
"By joining in with [the Auckland Council], and offering, whether it's financial, moral or technical support, you know, we're there for them.
"And we've been doing that all the way through."
He said it was important to lend whatever support was needed to get on with the plan and create more housing.