Thirteen members of Norway's International Standards Organisation (ISO) body, Standard Norway, have resigned over the country's approval for the controversial Microsoft OOXML document format.

Only two of the body's 23-member commit voted for the adoption - Microsoft itself, and Norwegian oil giant Statoil - but the Standard Norge management proceeded to recommended it against its member's wishes.

Confusion abounds about the reasons behind Standard Norway's adoption of OOXML (open office XML) against the wishes of the majority of its members, but the effect is to underline the global swell of opposition to the ISO's OOXML decision from earlier this year.

The resigning members left a parting shot in the form of a letter, made public in translated form last week.

"Standard Norway chose to defy their own technical committee and vote yes to a specification that is immature, useless, and unworthy of being called an ISO standard," wrote the objectors. "Standard Norway has lost its credibility in the IT area from the way it has administered the process. Standard Norway has set its own commercial interests ahead of what is best for society, most feasible technologically, and what is professionally advisable," the letter reads.

The resigning members further claimed that Standard Norway had been unduly influenced by a clutch of submissions from Microsoft, and was in breach of its own rules.

The ISO's fast-tracking and subsequent approval of OOXML will go down as one of the most contentious in its recent history, with allegations being made that Microsoft brought pressure to bear on the ISO for commercial reasons.

As the XML-based document standard that underlies Microsoft's Office suite, OOXML is at a deeper level another battle line in the software confrontation between open and proprietary standards. Its detractors argue that open source document standards such as the already-approved ODF (open document format) are more in the interests of government software buyers, for whom ISO approval is essential.

The OOXML adoption have already upset a variety of countries from the developing world, including South Africa, Venezuela, Brazil and India, and at least one large software rival to Microsoft, IBM .