In a court order, U.S. District Judge James Donato in San Francisco appointed Hagens Berman Sobol Shapiro and Quinn Emanuel Urquhart & Sullivan with "some reservations" given the past "rocky relationship" between the two law firms.

"It is the court's expectation that the attorneys will treat this appointment as the start of a new day, and put behind them the conflicts that gave rise to these proceedings," Donato wrote.

The case involves a group of consumers who contend Facebook exploited user data to maintain its market power. The company has denied the claims.

Law firms routinely vie for sole or co-leadership roles in high-profile class actions, since such appointments by judges can help steer cases and earn firms bigger cuts of legal fees.

Hagens Berman partner Shana Scarlett and Quinn Emanuel partner Kevin Teruya, the two lawyers appointed to represent a prospective consumer class, did not immediately respond to messages seeking comment.

Representatives for Quinn Emanuel and Facebook declined to comment, and a spokesperson for Hagens Berman did not immediately respond to a message seeking comment.

Scarlett in recent court filings said Quinn Emanuel was not respecting her view as a leading antitrust attorney based on her gender.

Quinn Emanuel denied the claim, saying it has "worked very hard to be cooperative with all counsel on the case, including female counsel."

Both firms had been appointed co-counsel in 2021 by a judge who has since been elevated to a U.S. appeals court.

Donato started the appointment process from scratch in January amid quarreling between Seattle-based plaintiffs' firm Hagens Berman and 900-lawyer Quinn Emanuel.

The firms sought individual, sole appointment and not co-leadership.

Donato said in Tuesday's order that the designation of co-leadership was interim and that "further reports of dysfunctionality or breakdowns in the work relationship" would likely result in designation of new counsel.

The case is Klein v. Meta Platforms Inc, U.S. District Court for the Northern District of California, No. 5:20-cv-08570.

For consumer class: Shana Scarlett of Hagens Berman Sobol Shapiro; Kevin Teruya of Quinn Emanuel Urquhart & Sullivan

For Facebook: Sonal Mehta, David Gringer and Ari Holtzblatt of Wilmer Cutler Pickering Hale and Dorr

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(Reporting by Mike Scarcella; editing by Leigh Jones)

By Mike Scarcella