to take action if parents have made potentially libellous comments on websites, the Daily Mail reported Wednesday.
The NAHT says it receives hundreds of calls every week from teachers who are being "cyberbullied" - and the majority of complaints are about parents using the web to criticise teachers or heads.
In 2009, research by the Association of Teachers and Lecturers (ATL) and the Teacher Support Network suggested 15 percent of teachers had experienced cyberbullying, and it is believed this figure is growing.
"Parents have a right to express their views and complaints should be heard. Schools can only benefit from constructive feedback," NAHT general secretary Russell Hobby said.
"Too often, though, social networking sites are a medium for the unreasonable and the unprincipled, and have a momentum out of all proportion to reality."
The NAHT has now updated its guidance for teachers who think they are being bullied by pupils or parents.
It tells them how to contact various websites if they have been targeted and gives tips on how teachers should manage personal accounts.
It also urges headteachers to have clear rules about social networking sites. Facebook is one of the sites where parents are known to have posted comments, the daily said.
One parent who didn't want to be named admitted she used her Facebook page to write about the behaviour policy at her childrens' school, having repeatedly failed to get an appointment with the headmistress about her son being bullied.
She took out her frustrations on her Facebook page until the school warned her of legal action if her comments became libellous.
"These online discussions are simply a reflection of what is happening offline. Facebook has worked hard to develop reporting mechanisms that enable people to report offensive content," a spokesman from Facebook said.
Facebook says it disables any accounts that are found to breach its rules on bullying and harassment by intimidating others.
According to the report, a 24-hour counselling helpline called Teacherline set up in October 1999 for stressed teachers in England and Wales now receives thousands of calls a month.
Teacherline reports that teachers are four times more likely to experience stress at work than employees in other professions.
Teacher Support Network is another organisation which says it has seen a marked increase in calls and emails from teachers who have experienced online abuse.
More than a third of teachers who have reported cyber bullying say it has reduced their confidence and self-esteem.