Microsoft has accused IBM of being obstructive in its attempts to get Open XML certified as a standard. Open XML is the basis for the file format used in Office 2007 .

In an open letter posted on Microsoft's website, the company said IBM was the sole dissenter in a vote to make Open XML an internationally-accepted open standard. Microsoft had submitted Open XML to ECMA International , a standardisation body. ECMA formed a committee from many companies including Apple and Novell.

Microsoft said in the letter it had told the committee that other companies would be able to access Microsoft patents related to the standard in order to implement it. Corel and Novell have announced they will implement Open XML support in WordPerfect and OpenOffice.

OpenOffice's key format is ODF, or Open Document Format. Microsoft argues that its Open XML format can sit alongside ODF quite happily, something that IBM didn't seem to agree with.

"When ODF under consideration, Microsoft made no effort to slow down the process because we recognized customers' interest in the standardization of document formats," says the letter, written by general Interoperability managers Tom Robertson and Jean Paol.

"IBM led a global campaign urging national bodies to demand that [standards bodies should] not even consider Open XML...that Open XML should not even be considered on its technical merits because a competing standard had already been adopted."

The letter goes further, accusing IBM of "declare[ing] victory in blocking Open XML."

"IBM ignores the fact that the vast majority of...members chose not to submit comments and that most if not all issues will be addressed during the technical review still to come."