The CTU secretary Sam Huggard presented evidence to New Zealand Parliament's Foreign Affairs, Defence and Trade select committee.
Mr Huggard examined the progress on the PACER-Plus trade agreement.
He said taxes on goods from Australia and New Zealand support health, education and social services, for which there are few alternatives.
"One of those would be a consumer tax like a GST or a VAT, and in the end those taxes hit the poor much stronger than they hit people who are well-off."
"So, if a primary way of raising money is going to be one that negatively impacts on poor then that's not something we could ever support."
Photo: CTU Sam Huggard