Labour is accusing the government of bribing voters with ACC levy cuts.
The corporation on Tuesday reported a huge $4.9 billion surplus and the government is working on levy cuts for 2014/15.
Labour's ACC spokesman, Iain Lees-Galloway, says the cuts should be delivered now.
"The government has been gouging New Zealanders for years, now it's proposing to `give back' some of what it's taken in election year," he said.
"That's a bribe, no two ways about it."
Mr Lees-Galloway says the government talked up a crisis in ACC so it could push levies to artificially high levels as a back door route to a surplus.
ACC's annual report shows the $4.9b surplus was $3.6b ahead of budget.
It accepted 1.7 million new claims, from 1.3 million people, paying out a total $2.2b.
The financial result comes from more clients being rehabilitated to fitness, reducing estimated future costs by $1.2b; an increase in interest rates reducing the current value of future costs by $1.2b; and investments bringing in $920m more than expected.
The surplus means ACC can reduce the deficit between its assets and the lifetime cost of every claim on its books from $7.2b down to $2.3b, and leaves the corporation well on track to its goal of financial sustainability by 2019.
Chief executive Scott Pickering says ACC is now in the best financial shape it has ever been in, and the organisation will greatly increase its spending on injury prevention and customer service in the year ahead.
ACC is holding a public consultation process on its recommendation to reduce 2014/15 levies by $562m, while the government has signalled moderate cuts of $330m. It will decide on the final size of the cut after feedback from ACC.