Mr Key has promised that the "tax switch" will leave no-one worse off and the vast bulk of people better off.
But yesterday he began selling the need for bigger tax cuts for higher earners.
"We can be envious about these things but without those people in our economy all the rest of us will either have less people paying tax or fundamentally less services that they provide," he said.
"We will be making sure that all New Zealanders, the wealthy included, pay their fair share," he told Parliament yesterday.
"The rich, by and large, do not pay the top personal tax rate. Really wealthy people will probably find they are paying considerably more tax as a result of the Budget ... not less."