Sidley Austin is stuck facing a proposed class action accusing it, along with fellow law firm Tonkon Torp and a set of accounting firms and banks, of contributing to an alleged securities fraud by now-defunct investment fund Aequitas Management LLC.

U.S. District Judge Michael Mosman in Portland, Oregon, has shot down most of a motion to dismiss the suit, brought by Aequitas investors against law firms Sidley and Tonkon Torp; auditors EisnerAmper LLP and Deloitte & Touche LLP; and banks TD Ameritrade Inc. and Integrity Bank & Trust. The ruling, dated July 5 and entered in the public court record on July 7, refused to clear Sidley and its co-defendants of potential liability for allegedly helping Aequitas mislead investors.

Mosman's decision makes official a set of recommendations released in April by U.S. Magistrate Judge John Acosta. In addition to recommending that many claims remain intact, the magistrate found that some claims weren't laid out with enough specific detail. But the magistrate held that the Aequitas investors—represented by Hagens Berman Sobol Shapiro and Stoll Berne—should be allowed to amend the complaint to fix those issues.