The dissident republican group, the 32 County Sovereignty Committee, has accused the Sinn Fein leadership of "censorship and authoritarianism" and has urged grassroots activists at this weekend's ardfheis to support "freedom of speech".
At a press conference in Dundalk yesterday one of its leading members, Mr Francie Mackey, a Sinn Fein councillor in Omagh, Co Tyrone, disclosed that he had been expelled from the party.
Meanwhile, Republican Sinn Fein has said 16 members of Sinn Fein in the Republic have applied to join it.
A spokesman said 10 members of Sinn Fein in Dublin and six in Listowel, Co Kerry, disillusioned with the peace deal, had approached his party.
The 32 County Sovereignty Committee yesterday accused the Sinn Fein leadership of "a purge" to ensure that no critical voices were heard at the ardfheis.
Sinn Fein sources have said they do not expect widespread criticism of their strategy this weekend. Mr Mackey is the latest Sinn Fein member to be expelled for involvement in the committee. Sinn Fein says dual membership is incompatible.
Last week it expelled nine members in Balbriggan, Co Dublin, for the same reason. Technically, they have all been suspended for six months but sources on both sides agree that in practice the suspension will be permanent.
The Balbriggan and Omagh cumainn both have motions on the ardfheis agenda criticising the leadership. The committee said those expelled had been told they would not be allowed into the ardfheis.
"My only `crime' has been that I have challenged the illegal British claim to my country," Mr Mackey said.
"We disagreed with the leadership, and now they are trying to silence us and stop us making our case at the ardfheis. They are treating their own delegates like sheep rather than people capable of making rational decisions.
"Sinn Fein, the party which fought Section 31, is now engaging in censorship." Mr Mackey urged delegates at the ardfheis to propose and second the two motions which will fall otherwise.
Another of those expelled, Mr Joe Dillon, said the Sinn Fein leadership tolerated only stage-managed debate. "It is stopping democracy at every level. No group has the right to take over the republican movement in such a way and usurp it from within."
He claimed the Sinn Fein leadership had no right to accuse others of violating republican rules. "Gerry Adams has given the nod and the wink to a deal which removes Articles 2 and 3 and establishes an Assembly. That is a breach of republican principles and should lead to automatic dismissal."
Mr Dillon challenged the Sinn Fein president to "be at least as honest" as the Ulster Unionist Party leader. "I disagree with David Trimble politically but I respect him for stating his mind on the Stormont agreement. Gerry Adams should show the same courage and honesty and nail his colours to the mast."
It was ironic that the Sinn Fein leadership had no trouble sitting down at Stormont with the unionists and the British government, its traditional opponents, yet excluded and expelled loyal republicans.
In an apparent reference to fears that the Provisional IRA leadership might move against the committee, he said: "The IRA exists to challenge the foreign occupation of our country. It is not and should never be used as a militia to sort out internal discussions in the republican movement."