In a letter to the International Organization for Standardization (ISO), Brazil officials expressed disappointment over the group's decision to give its imprimatur to Microsoft's Office Open XML format following a vote of member nations.
In a letter, members of a Brazilian technical committee said the process that led to OOXML's ISO ratification was flawed, in part because not all participants were given enough time to make their views heard.
South Africa and India filed similar protests this week.
In April, 75% of ISO member nations voted to approve OOXML as a standard. 14% voted against the format and the rest abstained.
Microsoft officials have said OOXML's ISO ratification makes it easier for developers and end users to work with the format and documents created with it. It also makes Microsoft Office products eligible for government procurement initiatives that require open standards.
OOXML competes in the document marketplace with the Open Document Format, which previously won ISO approval. ODF is used in open source office productivity suites such as OpenOffice.org and IBM's Lotus Symphony package.
Microsoft is facing other troubles on the format front.
In the wake of its vow last week to add support for ODF to its Office products, the European Commission said it would examine the move with an eye to determining whether it will loosen the software maker's stranglehold on the desktop applications market.
The EC's announcement came within hours of Microsoft's pledge to add ODF support to its Office 2007 desktop applications suite, which uses a version of OOXML as its default file format.
Microsoft said last week that it would add support for ODF, as well as the XML Paper Specification, Adobe's Portable Document Format (PDF), and China's Uniform Office Format, to Office 2007 through a service pack slated for release in the first half of 2009.