The Government is defending the robustness of the Mighty River Power share sale process.
Opposition MPs say the registration process is flawed as anyone can be signed up and it throws into question the number of valid registrations.
As of Tuesday afternoon, 290,000 people had registered their interest in buying shares in Mighty River Power.
Labour Party leader David Shearer and Green Party leaders Metiria Turei and Russel Norman all say they have received emails informing them they have been registered, when they have not done so.
Mrs Turei says she was signed up fraudulently and the system should be fixed so such a thing cannot happen again.
However, the Prime Minister says he heard in a news report that Mr Shearer had expressed interest in registering for shares in Mighty River Power.
Mr Key says Mr Shearer was quoted saying he might be interested in buying shares because if the Government is going to sell them, they need to be kept in the hands of New Zealanders.
State-Owned Enterprises Minister Tony Ryall says the security systems work, in that those who register receive an email confirmation.
He says a valid IRD number and New Zealand bank account and address will be needed for the actual purchase of shares.
Finance Minister Bill English stands by the number of people registered and says he is satisfied the process is working fine.