The Labour Party says Finance Minister Bill English forgot about first-home buyers when he signed off changes on mortgage lending.
From October, banks can have just 10% of new home loans tied to borrowers with deposits under 20%.
However, Mr English said several measures have been introduced to ease the blow, such as a law change on Thursday allowing the Government to free up land.
Labour Party MP Phil Twyford said the Finance Minister only asked Treasury how first-home buyers would be affected, a month after signing a memorandum of understanding allowing the Reserve Bank to impose the restrictions.
Mr Twyford said the Government should have asked the Reserve Bank to temporarily exclude first-home buyers from the measure intended to cool Auckland's housing market.
However, Mr English said the effect of restrictions had been talked about for months, so seeking Treasury's advice was just a formality.