A long-term Canberra Liberals member says he has left the party in disgust because he was unfairly denied the right to vote in the coming preselection.
Belconnen businessman Ramon Montero says the party is ''dysfunctional'' and called for an inquiry into the management of his Northern Electorate Branch.
Incumbent Senator Gary Humphries said Mr Montero's treatment was ''outrageous'' and the preselection was a ''disgrace'' and a ''laughing stock''.
Party officials did not respond on Sunday to requests for comment.
Mr Humphries is being challenged for his No.1 Senate spot by former party leader and Legislative Assembly member Zed Seselja and the contest has grown increasingly bitter. Some members are angry they did not know the preselection would be contested until after it was too late to register to vote.
Mr Montero said he believed he had fulfilled the requirement to become a preselector only to be told the meetings he had attended had not achieved a quorum and did not count as qualifying meetings.
The decision will rule out many members of the Northern Electorate Branch.
''As a proud member of the Liberal Party, I went to the Canberra Liberals office in Civic to vote in the pre-polling for the party's pre-selection for the electorate of Fraser for the 2013 federal election,'' Mr Montero told Fairfax Media.
''I was surprised and disappointed to discover that I was not eligible to cast my vote because a number of Northern Electorate Branch meetings I attended did not achieve quorum.
''I am extremely upset about this.''
Mr Montero said he felt betrayed after supporting the party physically and financially. ''As a loyal member of the party I had the shock of my life to be treated this way and feel insulted,'' he said.
''I feel offended after all the work I put into the last local election and many others before, financially and physically.
''I attended those meeting in good faith, believing in our party.
''The president of the branch should have reported these failures to the management committee and there should be inquiry into the management of the branch.''
Mr Montero said he was going public because he wanted the broader electorate to know the party was ''dysfunctional''.
''The party has treated me with contempt and I am personally very hurt indeed,'' he said. ''I am a strong believer that the people of Canberra must know about it and how the party is dysfunctional now.''
Senator Humphries said party members should not be denied a vote in the preselection over a technical issue.
''This is absolutely outrageous,'' the senator wrote to Mr Montero.
''Each of these members went into the preselection process believing they were fully qualified to participate, only to discover that, because a technical issue had not been addressed by party officials, they are no longer eligible.
''This preselection was already a disgrace. It has now become a laughing stock as well.''
ACT Liberals president Tio Faulkner said he had sympathy for the members who had found out they were not eligible to be a preselector.
''It is disappointing for them, for me and for the party. However, the rules have been and can only be applied fairly across the board - we cannot bend and change after the event.
''This issue was discussed in depth at a management committee meeting where it was unanimously agreed that the constitutional rules must be followed. There is simply no way to bend the rules for people who, unfortunately, find out they cannot vote in the preselection.
''It is important to note that this happens at every council meeting and preselection. It is vital to note that this applies across the division and does not favour one candidate over another.
''In fact, Mr Seselja approached the returning officer to see if there was any way, within the constitution, that this could be addressed as some of his supporters found themselves in the same position. The answer to him is the same answer to everyone - the rules are there to protect all candidates, all members and the division.''