BRUSSELS, Belgium — In a major step toward new penalties against Microsoft Corp., Europe's antitrust regulators voted unanimously yesterday in favor of fining the world's largest software company for flouting a 2004 ruling, two people close to the case said.

The regulators backed European Union plans to penalize the company but did not discuss the amount of the fine — which they will do at another meeting next week, according to the sources who spoke on condition of anonymity because no formal decision has been reached.

The European Commission threatened in December to levy daily fines of up to $2.5 million against Microsoft for not complying with an order to supply rivals with "complete and accurate" information to help them develop software that works smoothly with Microsoft's Windows operating system.

Under the rules, the commission must consult regulators twice — once on the principle of the ruling and on the amount — before it announces the fine. Regulators agreed on the principle yesterday.

The commission declined to comment on yesterday's meeting. Microsoft said it was working to meet deadlines to fix problems with the technical information it is compiling so that rivals can better work with its ubiquitous operating system.

Microsoft said it has a team of 300 people working full time on a framework to supply the information. Six of seven installments have already been delivered, it said.

The EU has never before fined a company for failing to obey an earlier order.