United Future leader Peter Dunne has decided he will oppose legislation to set up charter schools.
The Government intends to have the publicly-funded private schools ready to operate by the start of the next school year.
As it stands, charter schools will not have to follow the national curriculum or be required to employ registered teachers, nor will they be subject to the Ombudsman's Act or the Official Information Act.
Mr Dunne says he has extreme concerns about parts of the proposed legislation, such as the exemption from the national curriculum and that a taxpayer-funded school system will not be obliged to use registered teachers.
The United Future leader says he does not think the charter school model is necessary to achieve the flexibility its proponents are seeking.
The Government still has the numbers to pass the charter schools legislation, with the support of the Maori Party.
Maori Party co-leader Pita Sharples says it backs the concept of charter schools and plans to use its bargaining power to push for their teachers to be professionally qualified.