"Discussions have started but we haven't had a formal request yet," Mr English told reporters at Parliament this afternoon.
"We'll wait and see what the analysis tells us. I just don't want to pre-judge the discussions with the bank."
The Government has a Memorandum of Understanding (MoU) with the Reserve Bank on which tools it can use to curb mortgage lending.
The MoU would have to be amended before an income cap could be introduced.
Last month, the Government said it could not rule out the policy as a potential response to cool the housing market and prevent "a bubble emerging".
It is already used in the United Kingdom, where most buyers cannot get a mortgage higher than 4.5 times their annual earnings.
If applied in Auckland, it would limit a typical family to a mortgage of no more than $400,000.