A Dutch court blocked ABN Amro's $21 billion sale of LaSalle Bank to Bank of America on Thursday, potentially hindering Barclays’ bid for ABN, the Netherlands' largest bank.

The sale of Chicago-based LaSalle was deemed illegal unless ABN can obtain the approval of its shareholders. The Dutch investors’ group VEB has so far refused to give ABN the green light.

The verdict could lead to penalties for ABN if the bank can’t sell LaSalle. But it may have a greater impact in the battle to take over ABN, which heated up when the Royal Bank of Scotland submitted an unsolicited bid to beat out Barclays. The Barclays bid depends on proceeds that the sale of LaSalle would generate. Now Barclays will have to revise or lower its offer for ABN.

The Wall Street Journal reports that Bank of America could possibly seek damages from ABN in U.S. courts. Lawyers for the American bank say they might be compelled to do so.

The Financial Times points out that this news will only increase uncertainty about ABN, which could affect employees and draw the attention of regulators.