Belgium ? Microsoft Corp. lost an appeal at the European Union’s Court of First Instance to get a landmark 2004 antitrust ruling and record $613 million fine overturned.

The EU court’s dismissal of the appeal forces Microsoft to comply with the 2004 order by EU competition regulators. It must share code with rivals and sell copies of Windows without Media Player, a move the EU argues will give consumers more choice.

Microsoft lawyers said they need to study the 248-page ruling before they decide on the next legal move. They have a right to appeal to the EU’s highest court, a process that could take months if not years. In the meantime, Microsoft officials said they will aim to heal relations with the EU and admitted the company may need to do more to comply with EU demands.