I see what you're saying but I don't see a contract with my signature on it. And I think that even in the USA there would be a matter of proof, even for the IRS. And I haven't been paid yet, I'm here only two months now.
The fact that haven't asked for such information should speak on their behalf. I know it's common for USA citizens to give a SSN number for income tax, I know it has a diffrent meaning.
But here an SSN number is your whole social and legal identity. I would be open to identity theft, do you understand what that would mean if I would to take such a risk? And if I would get in that kind of serious trouble and the police here would find out I had given my SSN to someone in the USA on the internet, boy, I'd be looking trough bars on top of that.
Greetz from Pommerlis.