We have a potential business customer who wants to open a bank account. The business is registered in the US. The owners of the business are Canadian citizens without a TIN. Can an account be opened with them as authorized signers? Do we have to do something different on the Beneficial Ownership form?

I know that authorized signers are not customers and that we're required to CIP the business entity.

The answer should be dictated by your CIP/CDD Policy and Procedures.

As noted on the model beneficial ownership form, FinCEN allows for the identification of foreign individuals as follows:

What information do I have to provide?
This form requires you to provide the name, address, date of birth and Social Security number (or passport number or other similar information, in the case of foreign persons) for the following individuals (i.e., the beneficial owners):

The form also notes. "In lieu of a passport number, foreign persons may also provide an alien identification card number, or number and country of issuance of any other government-issued document evidencing nationality or residence and bearing a photograph or similar safeguard."

Since you are required to verify the identity of beneficial owners, your procedures must state what type of foreign documents you are will to accept.