Liberal Democrat leadership contender John Hemming is locked in a row with party officials after they threatened to exclude him from a high-profile hustings event.
Mr Hemming, the MP for Yardley, has been told he cannot speak at a party conference this weekend.
The Liberal Democrats have offered every candidate the chance to address members, at the event in London.
It follows the success of the Conservative Party conference, which took place as the Tories were in the process of choosing a new leader.
Every candidate had the chance to speak, including David Cameron, the eventual winner. Conservatives believe the sight of a party having an open debate about its future was popular with voters.
Liberal Democrat officials have invited the media to attend this weekend's event to hear "Liberal Democrat leadership candidates" talk.
In a statement, the party said: "The candidates for the leadership of the Liberal Democrats will have their first opportunity to address party members directly this Saturday."
But when questioned, officials confirmed that only one candidate will definitely have the chance to speak - Sir Menzies Campbell, the acting leader and favourite to win the contest.
This is because only he has so far gathered the seven nomination signatures from Lib Dem MPs needed to become a candidate under the party's constitution.
A party official said: "It is only Sir Menzies at the moment, but this could change if other candidates get the seven signatures before Saturday."
However, Mr Hemming argues the ruling is unfair - because he has only had a few days to get his campaign underway, following Charles Kennedy's resignation as leader last Saturday.
He said: "We are in discussions about it, because I don't think it is reasonable."
Mark Oaten, the Lib Dem Home Affairs spokesman who has announced his intention to stand, and Simon Hughes, the party president who is expected to announce his intention to stand today, will also be barred from making a candidacy speech unless they can gather the seven signatures in time.
As well as the backing of seven MPs, candidates need 200 signatures from party members from at least ten different constituencies.
Mr Hughes's office confirmed that he would make a statement today confirming whether he would stand for the leadership.
The Southwark North and Bermondsey MP said he wanted to take soundings among fellow-MPs at today's scheduled meeting of the Lib Dem parliamentary party before making a decision on whether to make a second bid for the top job.
Meanwhile, economics spokesman Chris Huhne confirmed that he was "considering" making a pitch for the job.
Although he has only been MP for eight months, 51-year-old Mr Huhne was previously a prominent member of the Lib Dem group in the European Parliament. ..SUPL: