Ordinary working families could be $11,000 a year worse off because of policies the government has already introduced and changes about to be revealed in Thursday's budget, the Greens say.
The party has released research which it says proves inequality is becoming entrenched in New Zealand.
"Policies like increases in the cost of early childhood education, increased student loan payments and cuts to the training incentive allowance show hard-working middle and low income earners can be massively hit in the pocket," co-leader Metiria Turei said.
"Ordinary families are struggling to keep up."
The research takes into account the increase in GST, proposed welfare changes and cuts to the top tax rate.
"It shows families in the top 10 per cent income threshold are more than $12,000 a year better off," Ms Turei said.