SIPTU is calling for an inquiry into safety and security procedures at Dublin Airport.
The union is claiming that security passes have been issued to inadequately-trained workers brought in by CityJet to replace ground-handling staff engaged in an industrial dispute.
The union says such workers have been given airside access and are working in potentially dangerous positions.
It is demanding that secondary safety and security measures be implemented in such situations.
Aer Rianta has strongly denied the allegations, which the airports authority said are completely unsubstantiated.