Economist Shamubeel Eaqub says Labour's tax policy is a "soft, soft" approach to increasing taxes.
And he says now is not the time to be introducing "a raft of new taxes".
If re-elected, Labour says it will create a new top tax bracket for those earning over $180,000 of 39 percent.
The policy attracted criticism from the Opposition. ACT leader David Seymour said on Wednesday the tax change "won't raise anywhere near the $500 million Labour says it will".
"Jacinda Ardern likes to say we're all in this together, but Labour is picking on a small group of New Zealanders to fund the COVID-19 recovery," Seymour said.
Due to the amount of money New Zealand is borrowing as a result of COVID-19, Eaqub told Magic Talk's Road to the Election it was inevitable there would be tax increases.
"It's a soft, soft approach to increasing taxes," he told host Mitch McCann. "To those who are arguing that it's not going far enough, you've got to understand the context of where we're at."
After Labour released its policy, the Green Party argued there should be more wealth taxes and tax brackets. The plan failed to address "the growing wealth gap and inequality in Aotearoa", co-leader James Shaw said.
Eaqub said it wasn't the time to introduce a raft of new taxes.
"We are still going through this incredible recession - we're almost six months through this pandemic and we've still probably got years in terms of the economic pain."
He believes any further changes to New Zealand's tax policy should come at the next election, not this one.
Finance Minister Grant Robertson said under its proposed policy, Labour won't make any further increases on any income tax.
"This policy is about maintaining investment in important services that are so crucial for New Zealanders like health and education while keeping tax rates the same as they are now for 98 percent of people," he told reporters on Wednesday.
Eaqub said the focus should be on making sure businesses and jobs are saved as much as possible.
