WhatsApp is working on new feature “Group Invitation” The feature is currently under development mode. The Group Invitation Feature will let users Automatically block others from automatically adding to groups.
According to source, This new Group Invitation feature you remain in charge and avoid Automatically adding you to a group without your consent. Currently, users can be added to groups without their permission – but the new feature will allow users to change this in their privacy settings.
User can select the Group option to change if they are to be added automatically to group fro the Settings menu. From the Menu, Users can choose between everyone, only their contacts, or nobody being able add them to groups without permission.
This Feature simply works like this, If the admin of a group is unable to automatically add a WhatsApp user to a group, that user will receive an invitation to join the group which expires after 72 hours.
It will be available for Beta Tester before rolling out other Android users. While iOS it will be available in the next iOS update.