Secondary Principals Association president Patrick Walsh says the Government should cut staffing at the Ministry of Education, not in schools.
School sector groups are scheduled to meet Education Minister Hekia Parata on Friday to discuss new staffing ratios that will increase class sizes at most schools and save more than $70 million per year by 2015.
They will be urging the minister to find those savings from somewhere other than school's staffing entitlements.
They say the money could come from ministry staffing and IT projects, school property and extra funding for private schools.
Mr Walsh says the Government should not try to make savings from frontline teaching positions.
He says the Government could also cut its planned trial of charter schools and scholarships that send children from poor families to private schools.
Pushing NZ beyond OECD norms
Massey University education professor John O'Neill says the Government's new school staffing ratios will push New Zealand schools even further above the average for developed countries.
He says the new ratios could create classrooms with as many as five students more than the average for countries in the Organisation for Economic Cooperation and Development.
OECD figures show New Zealand primary schools have just over 17 children per teacher.
That is higher than the OECD average of 16.5 children and ahead of Australia, where there are 14.8 children per teacher.
New Zealand secondary schools are also above the average, with 14.5 students per teacher compared to the OECD average of 13.7.
Professor O'Neill says New Zealand is about to go even further beyond the OECD's averages.
He says some students might not be affected by larger classes, but children from Maori, Pacific, and low income families will be worse off.
The Secondary Schools Principals Association says increased class sizes could tarnish New Zealand's reputation as a good destination for international students.
The international student industry earns about $2 billion per year.
Association president Patrick Walsh says small class sizes are important for attracting international students to study here.