The Serious Fraud Office (SFO) says it is looking into allegations of fraud against individuals connected to Auckland Transport.
A manager at the Auckland Council-owned agency was fired last month as part of an internal investigation.
Auckland Transport has said the fraud claims relate to its road corridor maintenance business, which looks after more than 700 kilometres of the region's roads.
The SFO carried out out several search warrants on Thursday and has confirmed it is investigating.
Acting SFO chief executive Simon McArley says Auckland Transport referred the matter to his office after an internal investigation. He says no one has been arrested.
Auckland Transport is not commenting on the case.
Labour's Auckland Issues spokesperson, Phil Twyford says the agency has an obligation to explain the circumstances around the allegations, given the transport body spends hundreds of millions of dollars of public money every year.
Mr Twyford says an explanation does not need to cut across the SFO's investigation.
