A Dutch commercial court has ruled that ABN Amro cannot proceed with the $21bn (£10.5bn) sale of its US operations to Bank of America (BoA).
Judge Huub Willems ruled that the Dutch banking giant needed shareholders' approval before agreeing to sell La Salle.
The judgment triggers a potential lawsuit by BoA, which is being advised by Wachtell Lipton Rosen & Katz, using name partner Herb Wachtell, and Dutch independent Loyens & Loeff. BoA also receives a $220m (£110.45m) break fee as part of its agreement with ABN.
The case was brought by Dutch investor group VEB, represented by Hague-based firm Pels Rijcken & Droogleever Fortuijn. Lawyers argued that the La Salle deal was a poison pill and an attempt to circumvent an "unwanted bidding process" by a rival consortium to Barclays.
Ironically, Wachtell Lipton's name partner Martin Lipton is credited with founding the concept of the poison pill.
The rival consortium, which says it can offer £49bn for ABN, is made up of the Royal Bank of Scotland, Spain's Banco Santander and Belgium's Fortis and is advised by Linklaters, Slaughter and May and Spanish best friend Uría Menéndez, Willkie Farr & Gallagher, Cravath Swaine & Moore and De Brauw Blackstone Westbroek. But the rival consortium's offer was conditional on the La Salle deal being blocked by the court. The consortium now has until Sunday to make a bid.
Meanwhile, in the US, a group of ABN investors led by Halpert Enterprises filed a class action in a New York court that aimed to halt the La Salle sale.
The sale of La Salle, ABN's US arm, was announced on the same day that ABN agreed to be taken over for £45.5bn by Clifford Chance and Sullivan & Cromwell client Barclays.
On the La Salle deal, Davis Polk is advising the bank with Chicago firm Vedder Price, which has an historic relationship with La Salle. It is as yet unclear which firm would represent it in any litigation, although Vedder Price has denied it would act.