"One of the best ways of doing that of course, and I urge Grant [Finance Minister Grant Robertson] to get to this...is to look at much heavier regulation of the fees charged on KiwiSaver schemes."
Cullen said default schemes and tracking funds had "no excuse" for charging more than about 50 basis points for just "clipping the ticket".
"They are charging a lot more than that and that comes off the net return substantially to people on modest incomes."
The Government has already signalled it will begin a review of the nine default providers next year and fees will be closely look at as part of that.
Robertson told a finance industry conference earlier this month that the default provider review, which takes place every seven years, was a chance to take stock of the market.
"To understand what obligations should be on providers and have a look at those big issues like fees, like ethical investment, because it is the right time to do it and to make sure we are part of enhancing KiwiSaver."