The Enemalta Professional Workers' Union has called on Mepa and the health and safety authority to act against a concrete batching plant which the union said is operating illegally near Delimara power station.
It said the batching plant has created a dust mountain which is causing inconvenience and respiratory problems to the power station employees.
The union also said in a statement that it had decided in its annual general meeting that its members would boycott any new workers should they be engaged by Enemalta in violation of the collective agreement.
The union urged the corporation to explain its intentions to the workers with regards to the planned shutting down of Marsa power station and the privatisation of the Petroleum Division.