B-1, r. 3.1 - Code of Professional Conduct of Lawyers

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85. If a dispute arises between clients in a joint mandate, the lawyer must inform them that, if they consent, he can advise them with respect to the dispute or refer them to another lawyer.
The lawyer must stop acting for his clients in the joint mandate if the dispute is not settled within a reasonable time.
The lawyer may continue to act for one of them only if the rules set forth in sections 87 and 88 allow it.
O.C. 129-2015, s. 85.