I believe Kristin is correct. If they want to bill under the group NPI they must notify the insurance carriers first to be added/linked to that group. I know that is definite for Medicare. We actually have run into this before. The regular PT was going out for surgery so she wanted to hire someone to come in for 6-8 weeks while she was out. We were advised we had to completely credential the other PT with the group in order to have it billed under the group NPI & EIN. Otherwise they would have billed under their own NPI/Tax ID and add the new location to their file. Either way, it's not a simple process.