Billing For A Fellow Who is "Sub-Contracted" to the office?

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Recently the office I work for thought of an idea to "sub-contract" a fellow through another organization that is this person's primary "contract" for their fellowship. Both organizations are for mental health services. If I remember correctly, there are certain billing guidelines that need to be followed for those doing their fellowships. However, this is the first time I have ever heard of a place trying to "sub-contract" someone to do their fellowship some place other than where their primary location is. Supposedly, the primary location was going to pay us directly for this person doing their fellowship. Can someone lead me in the right direction of finding solid guidelines on the rules of billing fellowship? I know this situation may sound super confusing. It was for me when it was brought up in a meeting. Any help would be appreciated