Representatives from all the major parties in Ireland, north and south, have signed a document outlining their rejection of proposals by the London government to draw a veil over legacy killings.
Atrocities carried out by British forces and those carried out in collusion with unionist paramilitaries are to included in an effective amnesty.
Over a dozen members of the US Congress have also now signed a letter objecting to the British government’s controversial legacy plans. It is understood the letter will be presented to the British ambassador in Washington in the coming days.
Families of victims of the conflict on all sides hailed the signing of the all-Ireland all-party document in Belfast and Dublin as “historic”.
The document states that they collectively reject London’s proposals on dealing with the past.
John Teggart, whose father Danny was killed in the Ballymurphy massacre, said it was an important day.
“We have victims from all avenues of those who were murdered during the Troubles,” he said.
“Today we have cross-community groups, and all political parties on both sides of the border, this is the first it has ever happened.
“We thank those who made the effort – this is only the first step. This (legislation) can be stopped.”
Among the signatories included Fianna Faíl senator Mark Daly, Labour’s Brendan Howlin, Fine Gael senator Emer Currie, Green Party TD Patrick Costello, and Fianna Faíl’s James Lawless, as well as SDLP MLA Dolores Kelly and DUP MP Jim Shannon.
Billy McManus, whose father was killed in the loyalist attack on Sean Graham bookmakers, said there are plans to hold a demonstration outside Downing Street next month.
Mr McManus said the proposed legislation makes a “mockery” of the thousands of people who were killed during the Troubles.
“It dances on the graves of our loved ones who were murdered,” he added.
“Our voices definitely will be heard. We all stand together to ensure this legislation does not go through.”
Former Noraid director Martin Galvin, a prominent US Ancient Order of Hibernians member, is currently visiting Ireland to lend his support.
“I am meeting with as many groups as possible to get as much information as possible,” he said.
“Irish America, the Ancient Order of Hibernians, we are working on a congressional initiative as well as other things to get the word out about how serious this is.
“The British are intending to bury legacy justice forever along with their victims.”
Mr Galvin added that it is important that the US is “aware of this, particularly Congress, to put pressure on the British government not to do it”.
He also revealed that online meetings have already been held involving relatives of people killed during the conflict and members of Congress, including Philadelphia-based representative Brendan Boyle.
Mr Galvin said that the Congressman volunteered to “get signatures” and “circulate a letter”.
“That is now going around and we expect to get a lot of signatures on it, a number of them have already signed,” he said.
“And everyone who sees that letter knows that there is something seriously wrong with the proposals that the British are putting forward.”
Mark Thompson from Relatives for Justice (RFJ) added:
“The US is the most effective and perhaps the only way in stopping the British government’s amnesty proposals and RFJ has been engaged fully in terms seeking direct US intervention.
“These proposals will hollow out rights and protections enshrined in the Good Friday Agreement (GFA) - they’re a direct assault on the GFA, which could only have been achieved with US intervention and support.”