At the Sinn Féin Ard Fheis on the 2nd of November 1986, members opposed to the taking of seats in, and recognition of, Leinster House left the Mansion House conference and reconvened in Chapelizod at a meeting which formed the new party, Republican Sinn Féin (RSF). The group was led by Ruairí Ó Brádaigh, who was elected President (and remained in that role until 2009).
In a declaration in their Republican Bulletin soon afterwards, RSF stated:
[A] majority of the delegates to the 82nd Ard-Fheis of Sinn Féin have today voted to allow their elected representatives to recognise the 26-County Parliament at Leinster House and take part in its administration … [S]uch a decision conflicts with the two fundamental principles of such a decision conflicts with the two fundamental principles on which the organisation is based and which are enshrined in the Constitution of Sinn Féin, viz. “(a) That the allegiance of Irishmen and Irishwomen is due to the Sovereign Irish Republic proclaimed in 1916. (b) That the sovereignty and unity of the Republic are inalienable and non-judicible”
We, Irish Republicans who wish to uphold the basic Republican position enshrined in the Sinn Féin Constitution until today and meeting in public session declare as follows: We renew our allegiance to the Sovereign Irish Republic proclaimed in 1916 and which was endorsed by the morality of the people of Ireland, acting as a unit, in 1918.
The same document also includes an account of the events of the split.
The Clár agus Rúin of the 1986 Sinn Féin Ard Fheis is also available in the archive.