The Prime Minister believes it would be difficult for other parties to argue against the KiwiSaver changes National is proposing, and is keen to see some cross-party buy-in.

Campaign chair Simeon Brown earlier compared National's coalition partners to children.

The National Party plans to make KiwiSaver compulsory for all workers, if re-elected, as part of a suite of changes that would cost more than $1 billion over four years.