Labour has accused the Prime Minister of exaggerating the benefits to State 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 growth.
But Labour's SOE spokesperson Clayton Cosgrove says Mr Key would have a problem if private shareholders invested more in the companies to help them expand.
He says if the Government did not match that investment, questions would be raised about its 51% shareholding.