Sinn Fein has rejected new legislation which is supposed to give so-called "on-the-run" republicans an amnesty.
Sinn Fein MP Pat Doherty called for the law to be rejected
Party vice-president Pat Doherty said the legislation was "far removed" from what had been agreed during 2001 talks with the government at Weston Park.
He also accused the government of "sleight of hand" in that the law would grant amnesty to security forces who committed murder during the Troubles.
But the government said there was no other vehicle for dealing with OTRs.
A Northern Ireland Office spokesman said Sinn Fein were "deluding themselves", if they thought that there was.
Mr Doherty met Northern Ireland Secretary Peter Hain at Stormont on Tuesday and urged him to withdraw the legislation.
"We are now calling for it (the legislation) to be rejected and we are withdrawing from anything to do with it," he said.
Mr Doherty said Sinn Fein would also be advising republicans "on the run" not to seek registration under the legislation should it go through.
The plans cover up to 150 people wanted for crimes committed before 1998.
They would have their cases heard by a special tribunal and, if found guilty, would be freed on licence without having to go to jail.
Mr Doherty led a delegation of party members and victims' groups to meet Mr Hain on Tuesday to give their views on the Northern Ireland (Offences) Bill which is currently going through Parliament.
Sinn Fein initially welcomed it, but now realise it will not only give an amnesty to IRA members but also to any soldiers or police officers who committed murder during 30 years of violence.
Sinn Fein met Northern Ireland Secretary Peter Hain
Urging the government to scrap the legislation and "stick to what was agreed", Mr Doherty said: "There are no British ground forces on the run.
"It was sleight of hand and inexcusable to bring that aspect into the legislation. It was not agreed at Weston Park. And it is not acceptable and needs to be rejected."
Mr Doherty said Sinn Fein had been in contact with many of those "on the run" before making the decision to reject the legislation.
The SDLP also met the government on Tuesday.
Since the Northern Ireland Offences Bill was published in November, the party has been criticising Sinn Fein over the issue of collusion.
The SDLP leader, Mark Durkan, claimed what he called "an alliance of sleaze" had been formed between republicans and the British.
The Ulster Unionist leader, Sir Reg Empey, said the legislation "should be scrapped", but warned that government must not enter into any future negotiation with republicans which might result in "even worse legislation".
"This distasteful, side deal which should never have seen the light of day in the first place must now be consigned to the dustbin where it belongs, never to be resurrected," he said.
The proposed law would set up a two-stage process. First someone who will be known as the certification officer will decide if someone is eligible for the scheme.
This could be a paramilitary on-the-run, someone living in Northern Ireland who is charged with an offence before 1998 or a member of the security forces accused of an offence committed when they were combating terrorism.
The case would then go to a special tribunal, consisting of a retired judge sitting without a jury. The tribunal would have all the normal powers of the Crown Court but accused would not have to appear for their trial.
If found guilty they would get a criminal record but would be freed on licence. They would have to provide fingerprints and DNA samples to be granted their licence.
The scheme will be temporary but a precise cut-off period is not specified in the bill - instead its expiry is linked to the lifetime of the chief constable's historic cases review team, which is looking at unsolved murders during the Troubles.