Labour's taking a crack at the Minister in charge of KiwiSaver for ducking his responsibility to ensure funds are being invested legally.

Consumer Affairs Minister Paul Goldsmith has confirmed the law which makes it illegal to invest in cluster munitions does apply to KiwiSaver.

He said it's a matter for police when they don't.

A New Zealand Herald investigation this week found evidence of investments in the production of cluster bombs, nuclear weapons and land mines.

Labour's Grant Robertson said nearly half a million New Zealanders have money in default funds, and the issue needs cleaning up.

"Not only is there an outcry from the public on this, it's now been shown to be illegal as well."

Robertson said the police may well be interested, but Goldsmith should step up himself.

"I think it's a fairly basic responsibility of a minister to make sure that a fund that he's responsible for appointing is acting in accordance with the law."