Education Minister Hekia Parata is being accused of bullying after she told schools to keep politics out of their newsletters.
Labour says she would be better off listening to teachers about how best to teach children.
Ms Parata gave the warning when she spoke at the School Trustees' Association annual conference in Wellington on Friday, Radio New Zealand reported.
Teacher unions recently fought the government over its cost-cutting proposal to increase class sizes and cut teacher numbers - a policy that was subsequently scrapped - and schools used their newsletters to tell parents what they thought about it.
Labour's education spokeswoman, Nanaia Mahuta, says schools resorted to using newsletters because Ms Parata initially rejected their concerns about the impact the policy was going to have.
"Hekia Parata chose to follow Treasury advice on a policy that would have had a negative impact on children's learning," she said.
"Now she is adopting bullying behaviour and trying to drive a wedge between parents and teachers."