The ABA House of Delegates recently adopted Model Rule 8.4(g), which reads:
It shall be professional misconduct for a lawyer to engage in conduct that the lawyer knows or reasonably should know is harassment or discrimination on the basis of race, sex, religion, national origin, ethnicity, disability, age, sexual orientation, gender identity, marital status or socioeconomic status in conduct related to the practice of law. This paragraph does not limit the ability of a lawyer to accept, decline or withdraw from a representation in accordance with Rule 1.16. This paragraph does not preclude legitimate advice or advocacy consistent with these Rules.
Although MR 8.4 previously prohibited discrimination on these grounds in the course of representing a client (via a comment), 8.4(g) is substantially broader. Professor Volokh critiques the rule and its Constitutionality here. His colleague, Professor Bainbridge, claims that the rule is a product of political correctness. The drafting committee anticipated some of these concerns and pointed out that more than twenty states already contain anti-discrimination language in their ethics codes.
While I believe this is a very worthwhile debate, 8.4(g) is unlikely to be enforced absent egregious misconduct (even assuming states choose to adopt it). Lawyers generally take a very broad view of "legitimate advocacy," and the Rule contains a mens rea component. With lawyers not infrequently stealing from and cheating their clients, most state bars will have little interest in policing their members' speech, especially in contexts unrelated to their representation of clients. Nevertheless, it would not be surprising to see some lawyer or group of lawyers challenge the Constitutionality of these anti-discrimination rules. Stay tuned.