Allegations of bullying and a death threat need to be investigated by the Association of Secondary Teachers Ireland, the union's incoming president has said.
ASTI's General Secretary Pat King raised the issues at the union's annual conference yesterday.
Mr King said he had received a death threat and despicable references to his children and grandchildren on a website moderated by the union's members.
Philip Irwin, who takes over as president later this year, confirmed Mr King had raised the issue at a meeting of the union's executive in January.
However, he said he was unaware of any formal communication from the general secretary to the union's president and officers since then.
Mr Irwin said the matter needed to be investigated in line with the union's duty of care to its employees.
The current president of the union, Sally Maguire, declined to comment on whether or not the union would carry out an investigation.
She said the matter was now an internal one.