The user group is concerned that the planned withdrawal of the machine in 2003 and the ending of support in 2006 will be a heavy blow to businesses that have invested in the platform.
Peter Bradley, general manager at the HPCUA, said, "There is never a right time to cease support for a platform, but people have made investments based on HP's promises. There will be a lot of unhappiness about the situation.
"Major new investments have been made over the past year and IT departments that have bought HP3000s recently are going to be made to look very foolish."
The HP3000 uses a proprietary operating system called MPE. Companies could face major training costs as they are forced to move to new platforms. Cheap training, loans of development boxes from HP and deadline extensions are among the measures that could be called for at the meeting, said Bradley.
The meeting will take place on 5 February. Details are at www.hpusers.org.uk.
HP was unavailable for comment at the time of going to press.