You need to have a completed I-9 Form for every employee. The instructions that come with the form will tell you what acceptable documentation you need. There’s a lot of different things that will work.
You don’t have to call anything in, just keep them on file. And always keep your I-9 Forms for active employees in their own folder, not in the employee’s personnel file. The INS is authorized to come in and audit your I-9’s, but it would be an employee privacy violation if you let them go through their personnel file.