World Vision New Zealand estimates nearly $8 billion worth of goods associated with child and forced labour were imported in 2022.
It said that means households spent an average of $77 a week on goods linked to modern slavery.
These so-called "risky goods" are most often clothes and electronics imported from countries like China, Indonesia, Vietnam and Malaysia.
But the humanitarian charity said the goods can also include bananas, coffee, toys and furniture.
Spokesperson Rebekah Armstrong told RNZ the report used official import data and a US government method of assessing risk to make the estimates. She said the estimates were conservative and were likely higher in reality.
To address the problem, World Vision wanted the incoming government to legislate against modern slavery within its first 100 days in power.
Armstrong said the law should go further than businesses simply disclosing where "risky goods" were from and what they were.
"We want the government to introduce due diligence legislation, which means that companies have to identify, address and mitigate modern slavery in their supply chain".
She said the former Labour government was working on disclosure legislation. But reviews of modern slavery laws internationally showed disclosure alone does not effectively tackle the problem, Armstrong said.