Pupils at a Yorkshire academy could be banned from trips if parents post negative comments about the school on social media.
In a letter, Morley Academy said "personal or insulting comments" by pupils, parents and carers will result in the "full withdrawal of privileges".
One unnamed parent said it was "worse than being in the North Korean army."
Head teacher Leanne Griffiths said parents and carers were being asked to model appropriate behaviour.
Another parent, who did not want to be named, said social media was "freedom of speech".
'Breakdown in rapport'
She added: "What are we teaching our children if you can't speak out and say what you feel?"
Ms Griffiths said that students were not being "punished", but they would not be able to take part in visits outside of the school until any issues had been resolved.
She said where negative comments had been made online, then there had been a "breakdown in rapport" between parents and the school.
She added: "We would deem that breakdown in rapport to represent a significant risk and we would not want to put the student, or any other student or ourselves, in a vulnerable position until we re-establish that rapport."
Ms Griffiths said there had been "too many examples of inaccurate and deeply offensive comments" made on social media and the academy is working with police to stop this.