Mr Ian Paisley Jnr of the Democratic Unionist Party has said Sinn Fein's acceptance of the Belfast Agreement is proof that the document weakens the Union.
"The fact is that Gerry Adams and David Trimble are now campaigning hand in hand for the same agreement," he said. He claimed the Ulster Unionist leader had been led up the "garden path" by the IRA.
However, Mr David Ervine, the leader of the Progressive Unionist Party, the Ulster Volunteer Force's political wing, has welcomed Sinn Fein's decision and said it would eventually be seen as one of the most important in Irish history. But he said the British government's release of IRA prisoners to attend the special ardfheis had ridden roughshod over the feelings of the vast majority of people in the North.
The Republican Sinn Fein president, Mr Ruairi O Bradaigh, said that by accepting the agreement and deciding to enter the new assembly, Sinn Fein had broken every pledge it had ever made.
It had accepted partition and "abandoned the national liberation struggle", he said. "It remains only for them to act fully in collaboration with the British forces of occupation against those who continue the struggle." However, the UK Unionist leader, Mr Bob McCartney, said unionists in favour of the agreement were asking their followers to act against their own interests. Speaking at the opening of the United Unionist headquarters in Belfast, he said: "They will be going out to the pro-Union people of Ulster, shoulder-to-shoulder with the representatives of Sinn Fein/IRA and the SDLP, and asking the pro-Union people to commit political suicide. Political suicide, like the human variety, is irreversible."
Mr McCartney also described the Presbyterian Church's attitude to the agreement as naive and "lacking in moral courage".
The director of the SDLP's Yes campaign, Mr Mark Durkan, said the Belfast Agreement was "the best chance we have of leading our society out of the morass of the past".
"It allows us to advance the process of reconciliation in our divided society. It allows us to begin tackling the political issues which divide us, as well as addressing the social and economic agenda which united us. Above all, it allows us to determine together the future of our society and of our island."
The Workers' Party said paramilitaries and politicians opposed to the agreement were "prehistoric" and should be rejected by the electorate.
The Alliance Party called on the Rev Martin Smyth, the dissident UUP MP for South Belfast, to resign his seat. The Alliance spokesman, Mr Steve McBride, said: "He is hopelessly out of touch with his own constituency. People in South Belfast want this agreement to succeed. They know that the No men, the "no hope here" men, have no alternative to offer except further division and suffering."
In a positive development, Fermanagh District Council last night voted 17 to 3 to support the Belfast Agreement.