The Northern Ireland Unionist Party (NIUP) was a small political party in Northern Ireland. It was formed in January 1999 as a splinter party from the UK Unionist Party (UKUP). This split was caused by disagreement between the five UKUP members of the Northern Ireland Assembly. Four of the members disagreed with UKUP leader Robert McCartney’s policy of resigning from the Assembly should Sinn Féin become part of the power-sharing executive.