What, an invasion? Well, not that bad, but it is an area that employers need to protect themselves. From what? Identity fraud and unwittingly employing illegal workers.
In Terminator they used dogs to sniff out the “intruders”, the robots. We need to use a much more banal way – seeing their photo ID!
This might seem a bit doubting of “honest” employees (do such things exist??!) but it is to protect you, the employer.
Simply by taking a photocopy of their photo id and any visas, you can protect yourself from monsters taking on the identity of honest workers.