About 60 bus companies around the country are facing severe cuts to their operations after the ministry slashed their school contracts for next year and awarded them to different providers following a tendering process.
Many of the companies affected are small rural operators who Mr Cave said had been "carting the kids to school since the horse and cart days" and were now "wiped out".
He and the other operators said the ministry had awarded the majority of new contracts to two big providers, Auckland-based Ritchies Transport and Hamilton-based Go Bus, to the detriment of family businesses.
"They have divided and conquered and blindsided a lot of us," Neil Jamieson of Bethlehem Coachlines in Tauranga said.
Mr Jamieson said his company stood to lose between 60 and 70 per cent of its income despite his fleet of 55 buses passing an initial evaluation by the ministry. In identifying the company's suitability as a school bus operator, the ministry had given it a score of 85 points, when the minimum required was 30 points.
Mr Jamieson said he had invested millions of dollars training staff and upgrading vehicles to bring them into line with ministry requirements in the past two years, so he was shocked when the company lost school bus contracts it had operated for up to 22 years.
He believed the Bus and Coach Association had exerted influence on the ministry because its president was Craig Worth of Go Bus, and the vice-president was Andrew Ritchie of Ritchies Transport.
But the ministry defended its tendering process, saying it consulted with the transport sector on rules for the tender and ran open workshops.
"These workshops were designed to ensure all providers had access to impartial advice about submitting a tender to the ministry," said Anne Jackson, the ministry's deputy secretary of schooling.
She said the Bus and Coach Association had not been represented on the ministry's evaluation committee and an independent observer had overseen the process.
Go Bus and Ritchies also rejected any notion that the association had influenced their success in gaining contracts.
Don Richards, owner of the East Coast's Waipawa Buses which has lost all its 70 school bus contracts, said his fears were for the management of the routes. "It's hard to imagine that a new bus company that doesn't know the area, doesn't know the roads, doesn't know the schools, doesn't know anything locally, is going to manage it." Another rural operator said children who the ministry deemed lived close enough to school to walk, but who lived on main roads with heavy traffic and without footpaths, were also likely to suffer.
"We pick 20 kids up and don't charge them," the operator said.
"That's something we've done for their safety. That's the sort of stuff that doesn't happen with big companies."