May I take a new case if it will require me to sue a former client?

Maybe. Rule 1.9 allows a lawyer to represent a new client whose interests are adverse to a former client only if the matters are not substantially related, or if the former client consents. Rule 1.6 regarding confidences and secrets also might have some impact on the lawyer’s ability to undertake representation adverse to a former client. The rules require a lawyer to make very specific disclosures before obtaining client consent to this type of representation, so please call the Ethics Helpline at 404-527-8741 or 800-682-9806 to talk about your situation with us.