The SDLP has suffered a series of resignations after ratifying its partnership with Fianna Fail.
The chairpersons of the party’s youth, women and LGBT+ wings said they were stepping down in an open letter that was sharply critical of how the decision was reached.
On Saturday, leader Colum Eastwood hailed the birth of a policy partnership he said would build for a better future in the years ahead.
The link-up with Ireland’s opposition party was endorsed by more than two to one of those present at a special conference in Newry, Co Down.
An alternative motion opposing the partnership was defeated.
Matthew Corr (youth), Caoimhe McNeill (women) and Matthew Carson (LGBT+) wrote: “Calls for respect and party unity ring hollow when a coach and horses has been driven through the proper procedure which exists to facilitate a debate, on equal terms, and allow the party to come together after.”
They added Saturday’s conference was called without proper notice being given.
“Voting opened while the debate was ongoing, allowing people to vote before they had heard all points of view,” the letter said.
“This was extremely discourteous to speakers of every side.
“There can be no reasonable debate when the terms of the debate are arbitrary and extra-constitutional.”
The party members said they would campaign for SDLP candidates in May’s local government elections.
“Our commitment to electing progressives who can make a difference to the lives of our people remains unwavering,” the said.
“But a line must be drawn – party members will not be treated like this without consequence.”