Based on the justifiable presumption that depositions in which a lawyer deposes the other side’s lawyer would inevitably cause hard feelings (or worse), many courts require lawyers seeking to take the adversary’s lawyer’s deposition to satisfy a three part standard articulated in Shelton v. American Motors Corp., 805 F.2d 1323, 1327 (8th Cir. 1986): (1) the information sought is not available elsewhere; (2) the information-laden communications sought are not privileged-protected; and (3) the "information is crucial." But courts disagree about the Shelton standard’s applicability to lawyers other than trial counsel.
In Allen v. Brown Advisory, LLC, Civ. A. No. 3:20-mc-00008, 2020 U.S. Dist. LEXIS 170513 (W.D. Va. Sept. 17, 2020), defendant served a third party subpoena on a Virginia lawyer who was representing the plaintiff -- but who was not acting as counsel of record. Defendant argued that the Shelton standard was inapplicable, but the court disagreed – holding that "an attorney need not be counsel of record in order to trigger the Shelton test." Id. at *7. The court also applied the Shelton standard to defendant's document subpoena -- noting that courts "have also found it appropriate to apply the Shelton test to document subpoenas served on counsel for an opposing party." Id. at *6.
Not all courts would be this protective, but lawyers tempted to seek discovery from other lawyers usually face an uphill battle.