PARENT-teacher associations could be in breach of charity law if they campaign to save or abolish the remaining 166 grammar schools.
Advice issued by the Charity Commission warns that their constitutions are likely to restrict them to discussing only the quality of education in the school.
The commission said a PTA could be justified in contributing to the debate about the abolition of selection if it had evidence that there would be a significant impact on the quality of education - but only at its own school.
The advice has implications for the PTAs in the grammar schools battling to retain academic selection.
The National Confederation of Parent-Teacher Associations advised parents involved in campaigns to set up separate groups.
Its 11,500 members have all adopted the standard NCPTA constitution, whose charitable aim is "to advance the education of pupils in the school".
And it said it was happy to provide individual advice.
Margaret Morrissey, NCPTA spokeswoman, urged schools to take up the offer and said: "Any school that is running a campaign should make sure it gets the right legal advice." Margaret Tulloch, from the Campaign for State Education, added: "There are going to be petitions and ballots. PTAs should get clear advice from the Charity Commission."