Teacher unions say the Government should not be propping up an ailing private school, with extra funding.
The Ministry of Education has so far given Wanganui Collegiate more than $800,000 in extra funding while it negotiates to become a state integrated school.
The money was provided at the discretion of former Education Minister Anne Tolley and is on top of its usual grant of about $800,000 per year.
The New Zealand Educational Institute and the Post Primary Teachers Association say the Government should not be helping a private school while state schools are told to make do with their funding level.
PPTA president Robin Duff says the funding arrangement is unprecedented.
But the Secondary Principals Association says it may be cheaper to support the school than to let it close.
A decision on the school's application is expected in August this year.
If it succeeds, its funding from the Government is likely to rise to about $3 million per year.