While the Education Review Office will survey schools to find out which ones had a particular issue with unhealthy food being sold, Health Minister Jonathan Coleman decided against a total ban on unhealthy food.
He did not believe the Herald DigiPoll survey result showed the public believed his plan was too soft on tuck shops.
Obesity was a complex issue, he said, and there was "no silver bullet". Better achievement in the areas of health and PE would make a difference.
"I note after I launched the Childhood Obesity Plan in October it was reported that the President of the Auckland Primary Principals Association was relieved that the plan didn't include any new forced requirements."
But Labour's health spokeswoman Annette King said the Health Minister was out of touch on obesity and the steps needed to reduce it.
The sale of unhealthy foods was virtually banned at schools - briefly - by the last Labour-led Government, but National repealed the rule in 2009 on grounds that schools should not have to be "food police".
Ms King said the next Labour Government would reintroduce mandatory requirements for school tuck shops.
"Obesity requires a multi-pronged approach. Part of the approach is education but also needs to include regulation and at times legislation.
"Mandatory tuck shop requirements must be part of a comprehensive approach. I'm delighted the majority of New Zealanders agree with tuck shop regulation, an approach Labour took in government."
Iain Taylor, president of the NZ Principals' Federation, a union representing more than 2300 principals, said it believed junk food should not be allowed in school tuck shops -- despite its members recognising that children would have access through nearby shops and family.
"We should be modelling good practices in the school ... we have to be a good model for any behaviour and activity."
After the Education Review Office survey of schools, those identified as having problems will be spoken to by Ministry of Health officials. Mr Taylor said he agreed with the Government's position that it was likely only a number of schools were selling junk food.
"I don't think there are many tuck shops these days that have fizzy drinks or cakes and chocolates. I can't even think of a school that sells fizzy drinks and bad stuff."
The Ministry of Education said it promoted healthy food and nutrition as part of the curriculum.
Schools were self-managing and made their own decisions about snack dispensers or tuck shops so it was unlikely the ministry would send a directive about what they should sell.
Thirty per cent of New Zealand adults and 10 per cent of children are obese, although the rates are skewed by ethnicity. Pacific people have the highest rate among adults, at 67 per cent. New Zealand has the third highest rate of adult obesity of developed countries.
