The party is calling for further reform of the EU and a return to the founding principle of free trade
The Ulster Unionist Party (UUP) has said they believe Northern Ireland will be in a better position if Britain stays in the EU.
The party's Executive has adopted a motion opposing a Brexit. Instead they are calling for the UK government to press "for further reform and a return to the founding principle of free trade, not greater political union".
However, the party says it "respects that individual members may vote for withdrawal" during the referendum on 23rd June.
Northern Ireland's Democratic Unionist Party (DUP) has already come out in favour of Britain leaving the EU, along with Secretary Theresa Villiers.
Sinn Féin, the SDLP and the Alliance party are all supporting Britain remaining in the EU.