State governments are guaranteed less than 20 per cent of the funding promised under the schools deal ripped up by the Abbott government, the Australian Education Union says.

The federal government said last week it would honour only one year of the school funding agreement, and allocate $230 million in 2014 to states that did not sign up to the scheme.

While the Abbott government insists it will maintain the same amount of funding for schools over the next four years that Labor had put forward, states that agreed to that Gonski funding deals say they risk losing their share of the funding.

Federal Education Minister Christopher Pyne is to announce the replacement funding model next year.

He has committed to maintaining a ''sector blind'' approach to school funding - which treats government and independent schools the same - only in terms of the extra money that disadvantaged children attract.

These loadings comprised 17 per cent per cent of Labor's additional funding package, the union said, putting rest of the previously promised money in doubt.

NSW and other states say they were told during a meeting on Friday with Mr Pyne that education funding will be cut, and those cuts will apply only to public schools.

NSW Education Minister Adrian Piccoli said ministers had been told existing legislation locked in federal funding for private, but not public, schools - placing government school funding rises at risk.

Australian Education Union deputy president Correna Haythorpe said by only committing to deliver about a fifth of the money on a sector-blind basis, Mr Pyne was signalling that he wanted to maintain the inequity of the current arrangements.

"This announcement by Christopher Pyne is totally at odds with the Coalition's election commitment not only to honour the Gonski agreements but also to ensure exactly the same funding, dollar for dollar, goes to every school,'' Ms Haythorpe said.

But Prime Minister Tony Abbott said his government had not broken an election promise to maintain the same amount of funding for schools over the next four years that Labor had put forward. ''This is a government which always keep its commitments,'' he said.

Mr Pyne accused the union of ''hysterical fear-mongering'', as 90 per cent of public school funding came from state governments. ''We inherited a mess from Labor: a model that is not national, not fair, incomprehensible and cut by $1.2 billion.''

Public Schools Left With A Fifth Of Funds, Warns Union