Rebel MP Geoffrey Donaldson was tonight ordered to support the leadership of the Ulster Unionist Party or face expulsion.
A motion was passed at the party’s 108-strong executive telling Mr Donaldson to toe the line or get out.
An angry Mr Donaldson tonight described it as a purge on the anti-Agreement wing of the party.
He said that there had been an orchestrated campaign of letter writing aimed at forcing him out.
The resolution was passed by 55 votes to 33 with four abstentions after a stormy meeting which lasted more than three hours.
Mr Donaldson said: “I believe that this represents a clear move against not only myself but against the anti-agreement members of this party. I believe this was orchestrated today, there were letters that came in which were repetitious and clearly that had been part of a campaign.
“This was quite deliberate. It was designed to target me specifically, to blame me for the poor election result of the Ulster Unionist Party.”
Tonight’s move by the party follows Mr Donaldson’s calls on David Trimble to resign after the party was overtaken by Ian Paisley’s hardline Democratic Unionists in last month’s Assembly elections.
The Lagan Valley MP now has a period of three weeks to support the party leadership or face disciplinary action.