Grant Robertson says National's "$4 billion gap" in its fiscal and economic plan calls into question whether the party could run the economy if it wins the upcoming election.
Earlier on Sunday Robertson, who is Labour's finance spokesperson, said National had used May's Budget figures instead of last week's Pre-Election Economic and Fiscal Update (PREFU) numbers - a difference of $4.3 billion - and had ultimately miscalculated how much it would save by stopping contributions to the Super Fund.
National's finance spokesperson Paul Goldsmith apologised for the error and called it an "irritating mistake".
"I never claimed to be perfect - I don't think any New Zealanders are," he said.
But Robertson said New Zealanders do expect perfection when it comes to running the Government's books.
"This draws into question whether they're in a position to be able to run the economy," he said.
"What is critical here is that they've made an error at a very basic level."
National leader Judith Collins said Goldsmith apologised for the mistake.
"Goldy didn't need me to tell him off," she said. "Goldy is a perfectionist and he hates to make any error at all."
Goldsmith said "we make mistakes from time to time".
Last election, it was Labour fiercely defending its numbers after then-Finance Minister Steven Joyce claimed there was an $11.7 billion hole.
Robertson denied on Sunday he was taking any joy in the error of his enemies.
"Not at all, in fact," he said.
The revelation of the error came the same day National launched its campaign. The mistake overshadowed its launch, which had already been a casualty of COVID-19.
It was held virtually due to restrictions on the size of gatherings, with only an 80-strong, socially-distanced crowd physically present.
"It was great. I really, really enjoyed it," Collins said of the launch. "It was professional, it was slick, it was fabulous, it was modern and it's now."