Ulster Unionist leader Tom Elliott will call for the creation of an official opposition in an Assembly debate later today.
Mr Elliott said he wants a review of government structures to include cutting the number of MLAs by 12 to 96.
The UUP leader also called for an "open and transparent" process to cut the number of quangos in Northern Ireland by a third by 2014/15.
"No one can question the need to review the structures that currently govern Northern Ireland," said Mr Elliott.
"In addition to the creation of an official opposition, we are also calling for a fundamental review of the number of departments and Assembly members and a re-structuring of so-called 'arms lengths bodies'."
Mr Elliott said the "expensive and bureaucratic system" does not deliver for the people who pay for it and the system by which candidates are selected is in need of reform.
Earlier at the weekend, the Fermanagh and South Tyrone MLA gave his first speech as leader at the UUP's annual general meeting in Belfast.
He promised to put in place new mechanisms to deal with candidate selection. These could include allowing the leadership to reselect candidates if they are unhappy with decisions made at a local level.
"We must again look at this process to ensure that rules will allow us to deliver the best winnable candidates," he said.
Looking back on his nine months as leader, Mr Elliott admitted the party has had a difficult year. Last month's council and Assembly election results were disappointing, with just 100 councillors elected and the loss of two MLAs.
"I don't run away from the fact that the Ulster Unionist Party has had a difficult few years," Mr Elliott told the meeting.
He then used some hard-hitting words to warn internal critics that if they ran to the media with their disagreements with party policy, he would not tolerate their behaviour.
Mr Elliott said: "Let me make something quite clear. I will hold to account any member of this party, be it an elected representative or an ordinary grassroots member, who thinks that they have the right to pursue their own agenda and damage the party."
The speech also urged party members to take some criticism "on the chin" and look to the future rather than trying to gain votes by pointing to the party's albeit more successful past.
Mr Elliott urged all party members to make an effort to take a united stand and deliver the party message with "one voice".
Tom Elliott was elected leader of the UUP in September 2010, defeating rival Basil McCrea. Since then there have been a number of departures from the party - including Harry Hamilton in Upper Bann, who joined the Alliance party, Paula Bradshaw and former international rugby player Trevor Ringland.