The agreement was widely rejected by trade unionists because it first gave the Republic of Ireland a role in the governance of Northern Ireland and because it had been excluded from the negotiations of the agreement. The Ulster Unionist Party (UUP) and the Democratic Unionist Party (DUP) led the campaign against the agreement, including mass rallies, strikes, civil disobedience and the mass resignation of all Unionist MPs in the British House of Commons. The DUP and UUP together gathered 400,000 signatures in a petition against the agreement. Northern Ireland Minister Tom King was attacked by Protestants in Belfast on 20 November.  On 23 November 1985, a mass rally against the agreement was held in front of Belfast City Hall, in which Irish historian Jonathan Bardon said: “Nothing like it has been since 1912.”  Estimates of the number of people vary: the Irish Times reported that 35,000 people were present;  The News of the World, the Sunday Times and the Sunday Express claimed 100,000;  Arthur Aughey, a professor of politics at the University of Ulster, said that more than 200,000 people were present;  and the organizers of the meeting said that 500,000 participated.  Even today, 30 years later, it is difficult to avoid concluding that unionism has still not understood the true message of the 1985 agreement: that London and Dublin will largely work together for Northern Ireland. And they will always find a way to cooperate, even if the UK votes to leave the European Union. The agreement established the Anglo-Irish IGC, made up of officials from the British and Irish governments. The body focused on political, legal and security issues in Northern Ireland, as well as the `promotion of cross-border cooperation`. It had only an advisory function – it was not empowered to make decisions or change the law.  The conference would have only the power to put forward proposals “to the extent that these issues are not the responsibility of a decentralised administration in Northern Ireland.” This provision should encourage trade unionists (who, through the conference, opposed the Irish government`s participation in Northern Ireland) in a deceded power-sharing government. Maryfield`s secretariat was the permanent secretariat of the conference, which included officials from the Ministry of Foreign Affairs of the Republic, headquartered in the suburb of Maryfield in Belfast. The presence of civil servants of the Republic has mainly outraged trade unionists.
[Citation required] Maryfield`s offices were closed in December 1998, after the Anglo-Irish Intergovernmental Conference succeeded the Anglo-Irish Intergovernmental Conference.  On 23 November, eight days after the agreement was signed, more than 150,000 people gathered in Belfast to protest. In a typically acerbic way, Paisley Thatcher condemned that he had signed the rights of the Loyalists. He also attacked Dublin: “Where do the terrorists return to the sanctuary? To the Republic of Ireland! And yet, Mrs Thatcher tells us that the Republic must have a say in our province. You never say it! never! never! The British House of Commons approved the agreement by an overwhelming majority and voted in favour by 473 votes to 47. Labour politician Jeremy Corbyn, a supporter of a united Ireland, voted against the deal and said: “We believe the deal strengthens the border rather than weakens it.” 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.