Hinshaw has a report on the California Lawyers Association Ethics Committee Formal Opinion 2021-1, which identified the "Elements of Effective Ethical Screens" that comply with the California Rules of Professional Conduct ("California Rules"). The Committee identified six mandatory elements of effective screens, along with several non-mandatory factors. The Committee noted that its opinion applies to circumstances where the ethical screen is implemented without client consent. Ethical screens implemented with client consent are governed by independent agreement rather than the California Rules. Go here to read the opinion or Go here for a summary of the opinion.