Labour Party leader Phil Goff says the National Party has no plan to stop foreigners buying the minority stake it intends to offer in some state assets.
If re-elected, National says it would sell part of the Crown's stake in four state-owned energy companies and reduce its shareholding in Air New Zealand.
Its leader John Key says a law could be passed limiting the shares an individual or company could hold.
During the final televised leaders' debate on Television New Zealand on Wednesday night, Mr Goff pressed Mr Key on how he could guarantee that no more than 10% to 15% of the shares would end up in foreign hands.
Mr Key replied that he has spent his life studying investment banking and knows how such things work.
After the debate he explained that the guarantee applies to the initial sale.
Mr Key made the point that other partial floats of New Zealand assets, like the sharemarket itself and Air New Zealand, have retained a majority New Zealand shareholding.