I don't see how this would be implemented at the ISP level
Simple: all new contracts with any ISP will require the customer to provide the internet ID.
All existing contracts have to be renewed no later than {date}, and if the customer fails to provide the internet ID by that date, he is forcefully disconnected.
With no details about the government's plan for an internet ID, we're left to our imaginations, which probably vary widely from person to person.