The vote of confidence was voiced in a letter to Massachusetts Secretary of State William Galvin last week and adds significant weight in favor of the decision, which has become the center of a political controversy.

The letter was signed by the American Library Association, the American Association of Law Libraries, the Association of Research Libraries, the Medical Library Association, and the Special Libraries Association, which together represent over 139,000 libraries in the US.

Dated December 12, the letter voices support for Massachusetts’s selection of ODF and warns against the dangers of storing documents in formats or media that are based on proprietary standards that may eventually become obsolete.

Documents created in ODF will remain accessible in the future because any programmer will be able to find its open, non-proprietary specifications, the letter stated. Requiring all Commonwealth employees to create documents in ODF will make it significantly easier for libraries to ensure that patrons 100 years from now will be able to read these historically important documents.

Secretary of State Galvin’s office is responsible for the State Records Center, the Massachusetts Archive, and the Public Records Division among other things, and opposes the plan to adopt ODF as a statewide standard, according to local reports.

The selection of ODF has proved controversial given Microsoft’s decision not to support the Oasis-approved standard, leaving Microsoft’s Office productivity suite out of the running for Massachusetts public sector contracts.

The company has responded by submitting its own Office Open XML Formats to the Ecma International standards group, and although Governor Mitt Romney’s office has responded positively to that move, it remains to be seen whether the Ecma standardization process will be open enough to see Office back in the running.

Massachusetts’ decision to select ODF has also prompted a Massachusetts Senate Committee hearing, proposed changes to the Massachusetts Information Technology Division’s decision making powers, and investigation into the actions of State CIO, Peter Quinn, who was recently cleared of any wrongdoing.

While welcoming Microsoft’s adoption of ODF, the five library associations have also urged Oasis to work to ensure ODF offers accessibility for disabled users, which has also been a sticking point.