Rule 1.7 of the Model Rules of Professional Conduct
Definition
Prohibits lawyers from representing clients with a concurrent conflict of interest against each other. The rule specifies that a conflict exists if (1) one client will be directly adverse to another, or (2) if the lawyer's personal interest or responsibilities to another client, former client, or third person creates a significant risk of materially limiting the lawyer's representation. The rule provides a limited exception that allows concurrent representation of clients with a conflict of interest provided (1) the lawyer reasonably believes he or she can provide both clients with competent and diligent representation, (2) the law does not prohibit the representation, (3) one client is not asserting a claim against the other in the same litigation or proceeding, and (4) each client gives informed consent in writing.