Some schools are using debt collectors to make sure parents pay "voluntary" donations.
Documents obtained by the Dominion Post show that some schools have been warned for not being upfront about some fees being optional, while other schools have been caught trying to withhold privileges until "voluntary" fees were paid.
By law, New Zealand children have the right to a free education from age five to 19.
However, some state schools say they can't survive on Government funding alone, so parents are asked for an annual donation, in addition to compulsory fees.
But the documents show the Ministry of Education has had to step in and tell some schools to stop some of their money-raising tactics.
Hastings' Karamu High School was reprimanded in September 2010 after a parent was told her daughter would not be allowed to buy a ball ticket or order a school leaver's jersey until donation money was paid.
Southland Girls' High School was warned for charging parents $60 to cover the cost of relief teachers during a school camp. A compulsory $90 "activity fee" was also disallowed.
A parent of a student at Wakatipu High School complained after receiving an invoice for unpaid fees and donations from debt collection agency Baycorp.
Schools' operational funding was increased by two percent in this year's budget, but Principals' Federation president Paul Drummond said funding hasn't kept up with actual costs and schools rely heavily on parents' voluntary support.
NZN