Eligibility for a 401k Plan for " employees" that have W-7#

I was asked today if a new 401k plan can cover employees with W7#s instead of SSN.  I have no idea and am not sure what information I need to get to make a determination.  Anybody have any experience or guidance on this?  Thanks!

I have not come across that question but it looks like the answer is yes, you can use the number issued from the W7.

https://www.irs.gov/forms-pubs/about-form-w-7

Correct, just need a valid tax ID# and that does not have to be a SSN.

In fact this is what a person is supposed to do to avoid things like what is in the recent thread about how to pay someone with a fake SSN.  

My understanding is even a person illegal in this country can get an ITIN for these kinds of purposes.