The South African Human Rights Commission (SAHRC) yesterday slammed the planned "chalk down" action by the South African Democratic Teachers' Union.
The SAHRC said the call, announced last week by the union, was an unnecessary step.
The statement follows a declaration by Sadtu that it would "turn every court appearance or disciplinary hearing of any of their members into a holiday".
This was on the eve of the appearance in the Vereeniging magistrates' court by Sadtu's two leaders Moss Senye and Sam Nengwekhulu on Friday. The two face charges of malicious damage to property and assault pertaining to last month's public sector strike.
Last week Sadtu's regional secretary Ronald Nyathi said: "It will be a holiday for all our members every time a leader or member of Sadtu appears in court or at a disciplinary hearing."
Nyathi also threatened to "deal with members who dare go to school on those days".
"They will be expelled from the union and dealt with in the harshest possible manner," he added.
SAHRC spokesman Lorraine Molepo said: "We are concerned about the call of action and are worried about the threat to members who do not adhere to the call."
Molepo said the action was planned at a critical time when attempts were being made through the education recovery plan to make up for the time lost during the strike.
Kate Bapela, spokesman for Gauteng MEC for education Angie Motshekga, said: "Teachers' unions signed an agreement to dedicate their time to the recovery plan. Unions must stick to the agreement."
Nyathi insisted that the call stands.