New Zealand First leader Winston Peters is demanding an explanation from the Education Minister -- after being barred from travelling on a school bus.

In a press release titled, "Minister throws Peters off bus", the MP for Northland said he was today scheduled to visit the Mangakahia Area School, which is at Titoki about 23km northwest of Whangarei.

The community there has been campaigning against the amount of dust thrown up from unsealed roads.

However, Ministry of Education officials informed organisers that the NZ First leader would not be able to join the children on their school bus, as planned.

He suspected that directive came from the National Party, that "will stop at nothing to thwart the Northland MP from doing his job".

"While we understand that there are safety issues of just anyone travelling on a school bus, it was important to be on the bus with the kids to see how the dust affects them," Mr Peters said.

"The Ministry informed the organisers at the last minute so we have to question what interference there has been at high levels in the decision-making."

Mr Peters said the Government had failed to take the families' concerns seriously, and the bus ban was a continuation of that position.

"Minister of Education Hekia Parata must provide answers as to today's appalling and disgraceful decision-making."

Jerome Sheppard, the Ministry of Education's acting head of the education infrastructure service, said its transport agent had been advised by Ritchies that Mr Peters wanted to travel on the bus.

"Ritchies had health and safety concerns about this. Under the terms of Ritchie's contract, they are not able to carry adults or any other ineligible passengers without our permission."

The bus is a 20-seater vehicle and Ritchies advised that it carried 20 primary and secondary aged students on it.

"Our transport agent advised us that carrying Mr Peters and other adults in his party would placed the company at risk of exceeding the limits of the Certificate of Loading and could mean not all children would get seats," Mr Sheppard said.

"As this request was made at such short notice, it wasn't possible to ensure that we could ensure the health and safety of the children on the bus under these circumstances. We informed our agent to turn down the request."

If more notice had been given Mr Peters may have been allowed on the bus, Mr Sheppard said.