The role of the FISO is to provide information to facilitate the safe movement of aircraft within an ATZ, and of vehicles and aircraft on the manoeuvering area.
A FISO is not permitted to control aircraft in the air, not even micro-control! and may not refuse entry to the ATZ.
They may control aircraft and vehicles on the prescribed parts of the manoeuvering area.
Pilots are required to make decisions for themselves at aerodromes with AFIS.