A probe is to be carried out after council workers were exposed to asbestos.
The discovery was made during maintenance work at the city’s Bridge of Don Academy on Thursday.
Asbestos materials were disturbed by building service workers during the removal of a panel.
The material – which was taken away for testing – has been confirmed as asbestos.
Unite regional officer Tommy Campbell said there is “great concern” that workers were contaminated with the material.
He said: “If the full health and safety procedures relating to suspected asbestos exposure were not followed by management these workers have left the site and run the risk of contaminating other workers and members of the public.
“Unite representatives have repeatedly made our health and safety concerns known about previous potential, asbestos exposure incidents.
“It beggars belief that we have yet another serious, potentially dangerous situation where the management have failed to respond properly in line with health and safety regulations and follow their own policies and procedures.
“Unite is demanding that a full and transparent investigation should be carried by the HSE, given the number of serious complaints the union has had to make over the past year to Aberdeen City Council.”
The council has confirmed it will make a full investigation and the Health and Safety Executive (HSE) is being notified.
A spokesman for the local authority said: “On Thursday a potentially harmful material was disturbed within a corridor at Bridge of Don Academy where work to improve security is being carried out during the school holidays.
“The area involved was made safe and sealed off and the material removed for examination.
“The material has now been confirmed as asbestos.”