Auckland Transport has called in forensic accountants from PricewaterhouseCoopers to help investigate the possible misuse of public money.
It comes two weeks after a senior manager at the council-owned agency was placed on indefinite leave while investigations into the potential misuse of money and serious allegations relating to road maintenance were carried out.
Auckland Transport says the matter relates to its road corridor maintenance business which looks after more than 7000 kms of the region's roads.
It says it has called in the accountants PricewaterhouseCoopers to help its own review of how it procures services.
Chief executive David Warburton couldn't say how long the inquiry will last, but says the agency is keeping both the Serious Fraud Office and the Auditor General informed.
No further information is being revealed by Auckland Transport, which cites legal reasons for staying silent.