The Green Party has become the third party to target changes to KiwiSaver during the election campaign, championing a "public option" provider as a way of saving money for scheme members.
Green co-leader Russel Norman launched the policy yesterday, saying a significant part of New Zealanders' savings were eaten away by costs and fees.
By offering a public KiwiSaver option, costs could be lowered, saving tens of thousands of dollars, he said.
"If these savings are reinvested,KiwiSavers' nest eggs will be significantly higher. We will do for superannuation what Kiwibank has done for banking. We will ensure there is a value-for-money public option."
The public fund could achieve fee and cost reductions through greater economies of scale, Dr Norman said.
The fund would be managed by the guardians of the $16 billion New Zealand Superannuation fund while Kiwibank or the Inland Revenue Department could provide the front-end management of individual KiwiSaver accounts.
Assuming a 40% saving in fees over the lifetime of a typical KiwiSaver, that could result in an increase of up to $142,000, or $64,000 in today's dollars, he said.
The recommendation for a single default provider was made by the government-appointed Savings Working Group in January.
The Australian Government announced similar but more sweeping changes to its superannuation industry in September, Dr Norman said.
The Greens' campaign kicked off in Wellington with an attack on Prime Minister John Key and his Government from actor Robyn Malcolm, who slammed his preference for photo opportunities over tackling environmental and social problems.
The Outrageous Fortune star denounced National for its lack of innovation, courage or social integrity, and for showing an "unshakeable and abiding love" of new roads and fossil fuels.
At the same time the party had demonstrated "a disregard for the 200,000 children living below the international poverty line", a "clear lack of understanding on how to support children's education", and a "dispassionate and punitive approach to those in our prisons".