The Manukau District Licensing Agency says event companies are deliberately breaking the law to make a quick buck by organising after-ball functions.
It is planning to stop alcohol being provided to minors at parties held during the school ball season over the next few months.
The agency started doing so at the weekend by removing alcohol from an event for Pakuranga College students. A van laden with alcohol was turned away from the function.
Inspector Paul Radich says it is becoming increasingly common for event planning companies to be organising after-ball parties with large amounts of alcohol.
Mr Radich says the minute the agency catches up with any of the companies, the police will be asked to press charges.
He says the charges could include sale and supply of liquor to a minor and unauthorised sale and supply.
Another five schools in the agency's jurisdiction are scheduled to hold balls in the coming months.
The Secondary Principals Association says schools have no power to interfere with after-ball parties because they are private functions.
President Patrick Walsh says parties are being organised in secret, with hundreds of students attending and large amounts of alcohol provided.
Mr Walsh says schools can advise parents about the dangers of after-ball parties, however, they have no legal power to shut them down.