FRANKFURT, GERMANY: A Microsoft document format that may be adopted as an international standard this weekend is a ploy to lock in customers, who could lose control over their own data in a worst-case scenario, critics say.

The International Organisation for Standardisation (ISO) is balloting its members on the issue in a vote that closes on Sunday. ISO approval would encourage wider adoption of the Microsoft Open XML format by public-sector organisations.

Opponents of Open XML, which is the default file-saving format in Microsoft Office 2007, say there is no need for a rival standard to the widely used Open Document Format (ODF) that is already an international standard.

They argue its 6,000 pages of code, compared with ODF's 860 pages, make it artificially complicated and untranslatable.

Microsoft and others point out that multiple standards are normal in the software and other industries and that competition makes for better products. Microsoft says its format has higher specifications and is more useful than ODF.

"More parallel standards makes for better standards. It's good not to decide for a single standard too soon," Michael Groezinger, Microsoft's chief technology officer in Germany, told Reuters in an interview.

He declined to speculate on the outcome of the ISO vote but welcomed last week's decision of the German Institute for Standardisation -- an ISO member -- to give Open XML a conditional "yes" vote.

At the heart of the controversy are fears that Open XML is not as open as it claims to be, raising the spectre that customers using the word-processing format could become reliant on Microsoft for access to their own documents.