When it is preplanned, the union may inform the management.
Courts have divergent views on the right to hold gate meetings. The management can obtain injunction from Civil Court against holding of gate meetings within certain distance from the factory premises if it can affect the movement of men and materials.
There is no law as such governing gate meetings. If the union is there in the organisation and wants to address members, it normally holds such meetings. If the union as a part of courtesy even asks for permission, no company would grant permission. Therefore normally such meetings are held outside the compound. However it should be ensured that the ingress and egress of men and materials is not disturbed nor the right to way is obstructed by any such meeting. The employees are also not permitted to leave their work and attend these meetings.
So, as precaution, you can send a letter of information to the nearest Police station about the gate meeting if you have any apprehension of law and order being disturbed, so that situation can come under control