Labour finance spokesperson Michael Cullen says a newly released report into KiwiSaver shows it is working for what he calls regular New Zealanders.
Dr Cullen was presenting an evaluation by the Inland Revenue Department, the Ministry of Economic Development and Housing New Zealand.
He said the most recent figures showed 827,000 people have joined the scheme since it was launched in July last year.
Dr Cullen said that was double the number originally predicted, and that the membership is representative of the overall workforce.
The evaluation shows 80% of KiwiSaver members whose earnings come solely from wages and salaries have a gross annual income of $50,000 or less.
Dr Cullen says that contradicts claims from critics who said many New Zealanders would not be able to afford the scheme.
He said while those who opt into the scheme tend to be on above-average incomes, those who are automatically enrolled are on below-average incomes.
Michael Cullen said National's policy to reduce the KiwiSaver scheme would hurt middle and lower income earners, who are the majority of KiwiSaver members.
National leader John Key said his party's proposed changes to the scheme would make it more attractive to New Zealanders, and encourage more people to remain in the scheme for the long term.
National has said if elected it would would cap the minimum employer contribution to KiwiSaver at 2% and remove the tax credit currently paid to employers.