The Federal Court has thrown the proposed $11 billion merger between betting giants Tabcorp and the Tatts Group into jeopardy at a hearing on Wednesday.
The Australian Competition Tribunal approved the deal with a minor condition earlier this year after Tabcorp and Tatts bypassed the usual testing of the deal by the Australian Consumer and Consumer Commission.
The Australian Competition Tribunal rejected the arguments of corporate bookmakers, Racing Victoria and its broadcaster Racing.com, who all made submissions objecting to the merger.
However, the ACCC appealed the Australian Competition Tribunal's decision in the Federal Court, which handed down its decision on Wednesday.
The Federal Court found in favour of the ACCC, setting aside the deal's approval and referring the transaction back to the Australian Competition Tribunal for further consideration.
Justice Nye Perram ordered the reason for the decision to be embargoed for five days.
The Australian Stock Exchange has suspended trading on both Tabcorp and Tatts Group shares until Friday to give both companies a chance to make announcements on the future of the merger.