A Dutch court ruled today that ABN Amro must freeze its $21 billion sale of US unit LaSalle to Bank of America, opening up the possibility of a rival bid for the Netherlands’ biggest bank. The commercial court in Amsterdam said the deal should be put to shareholders, as well as any other decision to sell the entire bank or parts of it.

At issue was whether ABN’s sale of LaSalle can be considered a “major transaction” requiring shareholders’ approval. Completing the sale is a condition of Barclays’ proposed 63.26 billion euros ($86 billion) takeover of ABN. But RBS, Spain’s Santander and Belgian Dutch Fortis have indicated that they are willing to pay more — as much as 72 billion euros — if LaSalle remains part of ABN Amro. Dutch shareholder group VEB, which asked Amsterdam’s commercial court for an injunction against the LaSalle sale, argued that the deal acts as a “poison pill”, making rival bids for ABN difficult.