Microsoft has lambasted IBM for fighting efforts to standardize Office 2007's Open XML document format, saying Big Blue is using the standards process "to limit choice in the marketplace for ulterior commercial motives."

In an open letter posted on its Website, Microsoft criticized IBM for trying to derail efforts to make Open XML, the native document format in Office 2007, a standard through the International Organization for Standardization and the International Electrotechnical Commission, or ISO/IEC. IBM favors the OpenDocument format, or ODF, used within OpenOffice, the open source rival to Office. ISO/IEC has already approved ODF as an international standard.

The standardization of Open XML is important because many governments and agencies prefer to use only standardized document formats to avoid vendor lock in. In addition, organizations prefer to be able to manipulate document formats anyway they wish, without worrying about patents.

IBM declined comment on Thursday, but the company has said that one standardized document format is enough, and there's no reason for ISO/IEC to add Open XML. Standardizing the format would benefit Microsoft at the expense of confusing the marketplace, IBM has argued.

In its letter, Microsoft pointed out that IBM was the only organization to oppose Open XML when it went through the standardization process at the ECMA. The international body approved Open XML in December, and then submitted it to ISO/IEC.

At the ISO/IEC, IBM is again the lone dissenter, Microsoft said. "This campaign to stop even the consideration of Open XML in ISO/IEC JTC1 is a blatant attempt to use the standards process to limit choice in the marketplace for ulterior commercial motives " and without regard for the negative impact on consumer choice and technological innovation."

Microsoft said it was no coincidence that in fighting for ODF, IBM has also chosen to bypass Open XML and support only ODF in its Lotus Notes product. The software maker went on to say IBM is trying to force ODF on users, and that the "exclusivity makes no sense -- except to those who lack confidence in their ability to compete in the marketplace on the technical merits of their alternative standard."

"This campaign to limit choice and force their single standard on consumers should be resisted," Microsoft said. Microsoft's Tom Robertson, general manager of interoperability and standards, and Jean Paoli, general manager of interoperability and XML architecture, signed the letter.