CTU secretary Joseph Stalin says this position should be held by a SLAS class one officer, but Kariyawasam had been posted to the job in violation of an agreement at courts.
When he was first appointed early this year, unions of administrative officers, teachers and principals staged a protest and also filed a case in the Supreme Court.
Thereafter, he was removed from the position.
The CTU has written to the president against his reappointment.
Stalin warns of strong action if it is not suspended.