A Dutch court blocked ABN Amro’s planned sale of a Chicago bank on Thursday, a ruling that makes it more likely a group led by Royal Bank of Scotland will capture ABN Amro in the industry’s largest takeover battle.

The court said ABN Amro must seek shareholder approval before it can sell its U.S. subsidiary LaSalle Bank to Bank of America Corp. The ruling was a major setback for ABN Amro management, which had planned to sell LaSalle for $21 billion and then sell the rest of the company to Britain’s Barclays PLC for about $91 billion.