A legal challenge to the Auckland Unitary Plan could "make the whole process grind to a halt", the city's deputy mayor says.

Photo: Supplied / ATEED

Lobby group Auckland 2040 and heritage advocacy organisation Character Coalition are seeking a judicial review of the plan's higher-density residential zones by the High Court.

A report prepared for Thursday's Auckland Council meeting said, until it was resolved, the legal action would have a major impact on some proposed housing developments.

Council staff said the action could freeze some zones for up to a year.

Read the report prepared for the council - including a list of appeals so far

Auckland deputy mayor Penny Hulse told Checkpoint with John Campbell the action was not unexpected but it was disappointing.

"This one has the potential ... to make the whole process grind to a halt."

Photo: RNZ / Claire Eastham-Farrelly

The two groups are challenging the legality of many of the higher-density zones, arguing they have gone beyond the scope of what could be decided by the plan's independent hearings panel and adopted by the council.

Council staff said the action would mean the city's old zoning plans would remain in force, and new development applications would be weighed up against both the old and new plans.

Ms Hulse said this would add "cost, time and complexity to the process".

"Obviously you can't build anything if you don't have reference to the zoning in which that sits."

She said the council did not want to spending huge amounts of ratepayer dollars fighting the appeal in court, and hoped to resolve the issue through mediation.

In total, 65 smaller appeals have been lodged with the Environment Court about the Auckland Unitary Plan. There have been 41 appeals on points of law to the High Court, and eight parties were seeking judicial reviews.