Gary Price was suspended from all council duties for five months in November after Powys council's Standards Committee ruled he had breached the code of conduct.
His appeal has been dismissed by the Adjudication Panel for Wales following a two-day hearing in Llandrindod Wells.
Mr Price has been contacted for comment.
He was found to have sent information which the council said "incorrectly and unfairly" portrayed what happened at a grievance appeal hearing, in which he was a panel member.
The Adjudication Panel for Wales unanimously agreed to refer the matter back to the Standards Committee with a recommendation that Mr Price be suspended for three months.
Council leader Barry Thomas said the decision "sends out a clear message that those who enter public office have to operate within the members' code of conduct and maintain the highest possible standards".
A decision to suspend a Powys county councillor has been upheld.