Vendors will have to reveal licensing costs in advance if they want proprietary technologies adopted as de facto standards as part of a formal standards-setting process, the European Commission has warned.

The message was delivered by EC Competition Commissioner Neelie Kroes in a speech to the Open Forum Europe conference.

Kroes urged standards bodies to demand 'ex ante' disclosure from vendors pushing to have proprietary technologies included in standards.

The Commissioner promised that her office would lend teeth to the demands. " This will almost always entail ex ante disclosure of the existence of essential patents [and] disclosure of maximum royalty rates," she said.

"Both can increase the effectiveness of the standard-setting process, lead to more competitive solutions and reduce the risk of later antitrust problems.

"If [standards bodies] need help in tightening up their rules to avoid being manipulated by narrow commercial interests, or to design the right ex ante rules, then they have my support."

The policy of ex ante royalty disclosure ahead of any standards-setting is obviously aimed at Microsoft, which has been battling to have its Office Open XML portable document technology adopted as a standard alongside ODF.

Kroes also told the Forum that choosing non-proprietary open standards is not just a smart business decision, but a "democratic duty" for governments.

"When open alternatives are available, no citizen or company should be forced or encouraged to use a particular company's technology to access government information," she said.

"No citizen or company should be forced or encouraged to choose a closed technology over an open one through a government having made that choice first. "

The speech was a rallying cry to software buyers, especially in central and local government, to deploy open source and not Microsoft's or any other proprietary software.

"It is simplistic to assume that we can fix on a standard today without paying attention to the risk of being locked in tomorrow," added Kroes.

The Commissioner has been locked in battle with Microsoft for years over the software giant's dominant position in the supply of software, continuing a war which dates back nearly two decades.

Kroes made reference in her speech to the fines levied on Microsoft recently for EC competition violations, but without naming the company.

The speech will have been a blow to any Microsoft executives hoping that the war with the EC was winding down.