Microsoft faces a tough battle starting Monday at a meeting in Geneva that will influence how widely the company's latest document format will be used in the future.

Representatives of national standards bodies worldwide will attend the ballot resolution meeting (BRM) held by the International Organization for Standardization (ISO). They'll be focused on revising the specifications for Microsoft's Office Open XML (OOXML), which the company hopes will become an ISO standard.

Although OOXML has already been approved by an industry standards body, Ecma International, the ISO designation is key, since governments look to the ISO when choosing technical standards.

OOXML failed to become an ISO standard during a vote last September, but it has another chance if enough countries can agree on the revisions. Those countries will then have one month to vote on the new specification after the BRM.

But Microsoft faces stiff opposition from companies and industry groups behind OpenDocument Format (ODF), which was approved by the ISO in 2006 as a standard. Those opponents contend that having more than one document standard makes software purchasing decisions harder for organizations.

In fact, those opponents are staging their own conference in the same venue in Geneva as the ISO meeting.

OpenForum Europe, an organization supporting ODF and open standards, has invited prominent OOXML critics and advocates of open standards to speak. They include Vint Cerf, vice president and chief Internet evangelist at Google and Hakon Wium Lie, chief technology officer of Opera, the Oslo-based browser developer.

The timing or venue choice wasn't a coincidence, said Graham Taylor, chief executive of OpenForum Europe. The organization has also timed its sessions to not conflict so BRM delegates can attend.

The shrewd timing is clearly aimed at sinking OOXML, which critics say is an overly complex standard and favors Microsoft in intricate, technical ways, even though the specification is open.

"We think there are a much wider set of issues that need to be considered by the national bodies when they come to make their vote," Taylor said.

Microsoft believes there is room for more than one standard. "We do not fundamentally believe that you have a uniform single view of technology ... in order to have interoperability," said Jason Matusow, senior director of interoperability, on Wednesday during a company event with journalists in London.

Microsoft also cites several projects under way to create translators to move formats from OOXML to ODF, and vice versa. However, Microsoft argues that the features of OOXML, a version of which is now used in Office 2007, are richer than ODF.

The meeting of the two sides at one venue has led some to speculate about heightened tension around what's already been an acrimonious debate. But Taylor said Microsoft representatives will attend OpenForum Europe sessions, and that there won't be any "heckling."

Taylor said he has assured the BRM conveners there will be no trouble. Press and observers can attend OpenForum Europe sessions, but the BRM is open only to official delegates from the 87 countries participating.

After the BRM is over, countries will look at the revisions to OOXML and then cast a vote. To become an ISO standard, a specification must win the support of two-thirds of national standards bodies that participated in work on the proposal, known as P-members. It also must receive the support of three-quarters of all voting members.