Community Housing Aotearoa chief executive Scott Figenshow has told councillors that the extra homes should improve affordability over time - but a 10 per cent affordable requirement "would give us affordable homes straight away".
Housing Foundation chief executive Brian Donnelly said developers would not actually build 422,000 new homes just because the plan permitted it.
"If you think density means that a whole lot of developers are going to race off and over-supply the market and bring prices down, that is naive," he said.
"Our experience is that, without these [affordable housing] provisions, what we see is the current lower-cost housing that is currently available in good locations now gets replaced with new, higher-quality, unaffordable housing.
"That ultimately forces people who are already close to their work to move out to the outer edges of the city. That puts more pressure on the transport infrastructure."
He said nurses, teachers and low-income service workers would be forced to either live far out of town or seek "Auckland loadings" on their wages.
In contrast, he said, cities such as Sydney, Adelaide, Vancouver and London all required a share of affordable housing in large-scale developments.
Most of the 154 Special Housing Areas created under the Auckland Housing Accord in the past three years have also required at least 10 per cent of new homes to be priced at below 75 per cent of the Auckland median house price - setting a current maximum price of $578,250.
The council's proposed Unitary Plan would have allowed up to half of the 10 per cent requirement in new developments to be "price-affordable" - below the same limit of 75 per cent of the Auckland median.
It would have required at least the other half to be "income-affordable", defined to mean that a household earning between 80 and 120 per cent of the median household income would pay no more than 30 per cent of its gross income in rent or mortgage payments.
"Income-affordable" homes could only be re-sold in the future to owners who would keep the homes affordable.
Councillors have the power to adopt "elements of both the proposed plan as notified and the hearings panel's recommendation", but must stay "within the scope of the submissions".