Waikato District Health Board says nine dairy owners and employees face possible prosecution after selling cigarettes to a customer under 18 years of age.
The DHB says 35 retail premises in Hamilton, Morrinsville, Matamata, Putaruru and Tokoroa were visited by its staff this month in a campaign to stop retailers selling cigarettes to people under the legal age.
It says staff at 26 of the dairies visited refused to sell cigarettes to the volunteer who gave their correct age, 16, when asked.
But nine dairies did sell cigarettes to the volunteer.
The DHB says reports on these cases will now go to the Ministry of Health.
It says the likely result will be a warning or a prosecution in the District Court.