The Labour Party has accused the Prime Minister of exaggerating the benefits to state-owned energy companies once they are partially privatised.
John Key says the companies will be able to expand overseas but Labour says they can already do that as SOEs.
The Government has argued that new capital injected into Mighty River Power, Genesis Energy, Meridian Energy and Solid Energy will boost their future growth.
The money that comes from the sale of shares will be put towards building new schools and hospitals.
Labour Party SOE spokesperson Clayton Cosgrove says Mr Key faces a problem: if private shareholders invest more in the companies to help them expand, will the Government match that investment?
Mr Cosgrove says if it won't, that would raise questions about what would happen to the Government's 51% shareholding.