The SDLP is to seek the recall of the Northern Ireland Assembly from its summer recess to address Westminster proposals to ban prosecutions for people involved in Troubles-related incidents.
The party’s deputy leader Nichola Mallon said the “British Government’s brutal intervention is hostile to the interests of victims and survivors and must be opposed”.
Proposals to end all Troubles prosecutions have been widely criticised by politicians and victims.
Northern Ireland Secretary Brandon Lewis said he intends to introduce a proposed statute of limitations which would end all prosecutions for incidents up to April 1998 and would apply to military veterans as well as ex-paramilitaries.
The proposals, which Prime Minister Boris Johnson said would allow Northern Ireland to “draw a line under the Troubles”, would also end all legacy inquests and civil actions related to the conflict.
Ms Mallon said: “To shut down justice and close off avenues for truth and reconciliation by providing an amnesty to state agents and paramilitaries involved in the most serious Troubles-related crimes, including murder, is absolutely abhorrent.
“These proposals are hostile to the interests of victims and survivors, they are opposed by all Executive parties and the British Government must withdraw them now.
“The SDLP has tabled a motion to recall the Assembly from its summer recess to address this matter and send a clear message to the British Government that we will not consent to this course of action.”
Northern Ireland’s political party leaders will meet Mr Lewis on Friday to set out their opposition to the UK Government’s plans.
DUP leader Sir Jeffrey Donaldson said a process had to be agreed which would allow victims to pursue justice.
He told the BBC’s Nolan Show: “We will oppose that legislation, as I think will all of the Northern Ireland parties represented in the House of Commons.
“The Labour Party are opposed to it. I don’t know if there will be enough Conservative MPs opposed to the legislation to be able to block it in the House of Commons because obviously the Government has a very large majority.
“But we have made our position clear to the Government, we want to agree a process that enables those victims and families that want to pursue justice to be able to do so, and I think it is wrong to deny them the opportunity of pursuing justice.
“We are, all the party leaders, meeting with the Secretary of State on Friday, so that will be an opportunity to make our views known.
“We cannot continue to fail victims, we cannot corrupt the rule of law. When you proceed on the basis that victims no longer have the opportunity to pursue justice, that is how they will regard this.”
The leader of the Catholic Church in Ireland said the proposals will be seen by many victims as a “betrayal of trust”.
Archbishop Eamon Martin said: “It is disturbing that victims and survivors, those have paid the highest price for the fragile peace we all enjoy today, once more feel marginalised and neglected.
“I was particularly disappointed by Prime Minister Boris Johnson’s naive comments in the House of Commons suggesting that his legacy proposals would allow Northern Ireland to ‘draw a line under the Troubles’.
“Dealing with the legacy of our shared past is not an easy task. It is a complex undertaking which belongs to all of us. It has no quick fix. No line can be drawn to relieve the deep hurt still carried in the aftermath of years of violence, death and life-changing injury.”