We will be speaking on this topic througout November, but here is a California case on the subject.  Its lesson:  the client confidence must be in issue.

"Case law does not “require dismissal whenever a law firm defendant suggests that client confidences are threatened,” Guilford wrote (.pdf). “Instead, they require a showing that the case can be tried fairly only by revealing client confidences. Irell represented the cable company and its chairman, uber-rich techie Paul Allen, in acquiring existing cable systems across the country. According to the tentative ruling (which had to assume the allegations are true), one of Irell’s associates mistakenly deleted two paragraphs of a contract, which led to Allen acquiring a type of stock he wasn’t supposed to. That forced Charter to pay Allen “millions of dollars” to undo the damage.

L.A.-based Irell tried to snuff the suit by arguing it could not defend itself without revealing Allen’s client confidences, over his objections. And while Guilford found that very well may end up the case, “the dust of initial posturing has not yet sufficiently settled” to determine whether Irell could mount a defense without breaking privilege.

The court found Irell had not yet pinpointed the specific privileged issues it needs to be able to discuss. "