The group has called on Scott McNealy, chairman, president and chief executive officer at Sun, to join a public debate on the issues.
Most users run Solaris on Sun's own UltraSPARC processors. However some businesses run Solaris on Intel chips.
In addition, some users have put Solaris on laptops and low-cost desktops instead of more expensive Sun gear.
In the past, Sun has offered free downloads of earlier versions of Solaris for Intel-based systems. However, in January Sun halted development on Solaris 9 for Intel chips as a cost-cutting measure.
Last month it made Solaris on Intel available as a product, but only on its Sun LX50 server. For the last nine months users have called for Sun for to make Solaris 9 available on a wider range of Intel-based hardware.
In an open letter published in the San Jose Mercury News, the Save Solaris Organisation stated: "Mr McNealy is being challenged to support his company's actions and subsequent decision making with respect to a large community of Sun customers. Mr McNealy has earned a reputation for flamboyantly berating his competition. His loyal customers have earned the opportunity for an open forum."
The letter charged Sun with failing to communicate with its user base and act in users' best interests.
Sun has been meeting with a group of users, known as the Secret Six, during the past nine months to discuss ways in which non-Sun developers might help out with bug-fixing and writing drivers for Solaris on Intel.
The company has also suggested producing an edition of Solaris that would be maintained in part by the user community.
"We are still very engaged with the community to figure out a solution that makes business sense for Sun," a spokesman said.
Sun declined to say whether McNealy would accept the challenge to a debate. However, the Sun chief executive recently said the company had addressed the needs of most of its customers by providing Solaris 9 on the LX50 server.