Per policies set by VUMC leadership, we have to engage in compliance checks with all entities with whom we have business relationships.  Per the policy, this includes no-money agreements and even CDAs. The vendor who performs the compliance checks uses the other party’s EIN (tax ID number) as the unique identifier for this purposes, and the W9 is an easy way to collect the EIN. If the other party does not want to provide the W9, but is willing to give us their EIN, we can enter it for you.

Any entity cutting checks to U.S. employees has an EIN.  W/o the EIN the employees would be unable to file income taxes.  Government agencies, therefore, have EINs or "Tax ID numbers" even though the agencies themselves aren't paying taxes.