Labour was proposing a tax-free threshold on the first $5000 of wages and removing GST from fresh fruit and vegetables.
Mr de Raad said that would cost about $1.7 billion in the first year, to be funded by raising the top tax rate for high-income earners.
"From an economic perspective, these proposals would be a big step backwards.
One of the big concerns is what raising the top tax rate would do to New Zealand's attractiveness as a place to live and work."
A new tax rate at $100,000 per annum would have to be 53% - affecting around 131,000 people - to fund the $1.7 billion, he said.
Introducing exceptions to the broad GST structure would be inefficient as well.
New Zealand already had a welfare system to target low-income households.
If the aim was to assist those households, the policy focus should instead be on economic prosperity and reforming costly and inefficient welfare policies, such as Working for Families, costing $2.8 billion a year, Mr de Raad said.
The proposal would make the tax system less competitive. Introducing a tax-free threshold by increasing the top tax rate would be harmful to the tax system, he said.
A New Zealander earning $150,000 would be $150 a week worse off in New Zealand than they would earning the same income in Australia, rather than $17 a week better off in New Zealand at present.
The removal of GST from fresh fruit and vegetables would cost nearly $250 million and benefit the poorest 10% of households by a "paltry" $1.50 a week, Mr de Raad said.
Taxes affected the decision by households to work, buy and save.
All tax systems suffered from inefficiencies, called "dead weight losses".
However, broad-based taxes, such as GST in New Zealand, minimised the dead weight loss.
"Removing GST on fresh food would increase enforcement and administration costs for both the government and businesses.
"It would create a favourable bias towards fresh food, which is healthy.
"But it is unclear if the benefits would outweigh the additional costs."
There were likely to be more cost-effective, better-targeted approaches to improving diets, he said.
At a glance:
• The $5000 tax-free threshold would cost $1.5 billion.
• A top tax rate of 53% starting at $100,000 would be needed to pay for the tax-free threshold and removing GST from fresh food.
• The required top tax rate would rise rapidly as the threshold was increased.
• The exodus of more skilled labour to Australia would probably increase.
