Education Minister Anne Tolley has asked the Auditor-General to investigate a school bus tender process which has left many bus operaters angry and concerned for their futures.
Ms Tolley says concerns about the propriety of the tender process can be allayed only by having an independent body test their validity.
Operators complained several weeks ago that the Ministry of Education's process was run in an unfair and illegal manner.
The ministry defended its process, saying the companies given the new contracts would provide a safe service and a more environmentally friendly fleet.
The ministry's figures show that nationwide, four main bus companies - Ritchies, Go Bus, Tranzit and Madge Coachlines - won almost half the tenders and were allocated hundreds of school runs.
Most operators received six runs or fewer.