American Bar Association Model Rules of Professional Conduct - Rule 1.17. Sale of Law Practice
A lawyer or a law firm may sell or purchase a law practice, or an area of law practice, including good will, if the following conditions are satisfied:
(a) The seller ceases to engage in the private practice of law, or in the area of practice that has been sold, [in the geographic area] [in the jurisdiction] (a jurisdiction may elect either version) in which the practice has been conducted;
(b) The entire practice, or the entire area of practice, is sold to one or more lawyers or law firms;
(c) The seller gives written notice to each of the seller's clients regarding:
(1) the proposed sale;
(2) the client's right to retain other counsel or to take possession of the file; and
(3) the fact that the client's consent to the transfer of the client's files will be presumed if the client does not take any action or does not otherwise object within ninety (90) days of receipt of the notice.
If a client cannot be given notice, the representation of that client may be transferred to the purchaser only upon entry of an order so authorizing by a court having jurisdiction. The seller may disclose to the court in camera information relating to the representation only to the extent necessary to obtain an order authorizing the transfer of a file.
(d) The fees charged clients shall not be increased by reason of the sale.