The Labour Party is questioning why the Accident Compensation Corporation wants to spend nearly $1 billion on a high risk technology upgrade.
The ACC wants to make its computer systems more efficient as part of its Shaping Our Future project which is forecast to cost up to $950 million over 15 years.
ACC said the project would result in better customer service.
But Labour's ACC spokesperson Sue Moroney said the Government had a track record of cost blowouts when it comes to IT upgrades - and she expected this would be the same.
"What we need, if ACC truly wants to have more trust from the public, then they need to make sure that Government stops overcharging for ACC levies.
"And they need to get some consistency on ACC decisions, that doesn't come close to a $1 billion of money being spent on it."
However, ACC Minister Nikki Kaye said the estimated yearly costs of the Shaping Our Future programme would not necessarily exceed what ACC already spends each year on change and technology.
"However, because of its significant scale my expectations of the ACC Board are that there are robust processes in place regarding design and monitoring, including by the Government Chief Information Officer and Treasury," the Minister said.
A self-assessment by ACC found its Shaping Our Future technology project was high risk.