Official figures show the average household would have to spend a large part of its cash savings to buy shares in the first power company float.
The Government is selling up to 49% of four state-owned energy companies, of which Mighty River Power will be the first.
Statistics New Zealand's 2006 Survey of Family Income and Employment, the most recent available, shows the median household has $1700 in the bank - not much more than the $1000 the Government has indicated will be the minimum investment in Mighty River Power shares.
Labour's state-owned enterprise spokesperson Clayton Cosgrove says that makes a mockery of the Government's claims about the widespread ownership of the shares.
"The average Mum and Dad's got to keep the money there, in case they need it for a contingency.
"The people who will buy these shares, as we know, will be the big institutions and those with a lot of discretionary income."
However Finance Minister Bill English believes the partial asset sales will make it easier for those on lower incomes to become wealthier.
"They may only have $1700 in the bank but they are working pretty hard to pay off mortgages or trying to save up a bit while they're renting.
"This kind of investment may give them an opportunity to own something that is more accessible than home ownership, which is generally at the top of their list."
Mr English says most New Zealanders don't feel that they own the assets of the Government and selling shares to KiwiSaver funds and through the sharemarket will give them a more direct stake.
Parliament on 26 June passed the Mixed Ownership Model Bill which allows the Government to partially sell state-owned energy companies Genesis Energy, Meridian Energy, Mighty River Power and Solid Energy.