Within Northern Ireland, the agreement was largely unpopular. The Unionists strongly opposed it, as Mr Thatcher did not include them in the negotiations. They also opposed the proposed IGC, fearing that Dublin would have a hand on the levers of the Ulster government. November 17, 1985 in Hillsborough, Co. Down, signed by Margaret Thatcher and Irish Prime Minister Garret FitzGerald. The agreement should promote reconciliation in Northern Ireland and cooperation between the British and Irish governments. The Ulster Unionists saw it as a form of common authority, and in 1985/6 they waged a fierce opposition campaign. The Anglo-Irish Treaty of 1921 (Irish: An Conradh Angla-Eireannach), commonly known as The Treaty and officially the Articles of Agreement for a Treaty Between Britain and Ireland, was an agreement between the government of the United Kingdom of Great Britain and Ireland and representatives of the Irish Republic that concluded the Irish War of Independence.  It provided for the creation of the Irish Free State within one year as a self-administered regime within the “community of nations known as the British Empire,” a status equivalent to that of “the Dominion of Canada.” It also provided Northern Ireland, created by the Government of Ireland Act 1920, with an opportunity to express itself from the Irish Free State it was exercising.
The excessive language of politicians, the threats of violence of Protestant gunmen, who have a plethora of weapons, and the gloomy mood of the entire trade union community, from university intellectuals to unemployed workers, do not bode well for the reconciliation of the two northern communities, which is ideal for reaching the agreement. When the two governments worked on the agreement, there was no reason to doubt the words of Barry White, an editor of the Belfast Telegraph and a respected observer of the Nordic scene, who had written a few months earlier: “Protestant trade unionists in Northern Ireland and Roman Catholic nationalists were never further away.” The agreement was adopted by Seanad Iireann by 88 votes to 75 and by 37 votes to 16.   The Irish nationalist Fianna Féil party, the main opposition party in Ireland, also rejected the agreement. Fianna-Fiil leader Charles Haughey said the agreement was contrary to Articles 2 and 3 of the Irish Constitution because it had officially recognised British jurisdiction in Northern Ireland.