Northern Ireland Secretary Peter Hain has accused the Conservative Party of abandoning a cross-party approach to the peace process.
Mr Hain said the Tories were not showing support
He has urged new Tory leader David Cameron to co-operate.
Mr Hain said it was a "great shame" that the Tories opposed "essential building blocks" of the deal, such as an amnesty for fugitive IRA prisoners.
But the Tories say that amnesty would allow "barbaric murderers" to "go free without spending one day in prison".
Mr Hain said the government was entitled to the same level of support Labour had given John Major in the early 1990s.
Dealing with "on the runs" - as the fugitive prisoners are known - has been one of the major stumbling blocks to the reinstatement of devolved Northern Ireland institutions.
They have been suspended since the "Stormontgate" spying scandal of 2002.
In an interview published on the website ePolitix.com, he said: "I think there is a need for more inclusivity on the floor of the House of Commons.
"It's not to say you can't have an argument over a detail in a bill, but when it is an essential building block to getting peace then we are entitled to their support, having backed them on similar, if not even more controversial, moves."
Mr Hain is angry that the Conservatives are opposing the Northern Ireland Offences Bill which would allow an amnesty for terror suspects who had never faced trial for alleged offences committed before the 1998 Good Friday agreement.
Freedom for fugitive IRA prisoners has been a stumbling block
"The opposition parties used to support the Government, as we did when we were in opposition and John Major started talking to the IRA," he said.
"We supported him and it was a tough thing to do; people didn't like the fact that we supported the Government when the IRA had only recently being setting off bombs.
"They set off the bomb in Canary Wharf after his Government started negotiating with the IRA, and we still backed the Tories' dialogue with them."
He said: "It is a great shame that the bipartisan policy which helped deliver peace and stability - unparalleled peace and stability for Northern Ireland - should have been broken by the opposition in recent years."
Shadow Northern Ireland Secretary David Lidington told BBC News the amnesty was opposed "not just by Conservatives - but by Liberal Democrats, by both unionist parties and nationalist parties, like the SDLP, in Northern Ireland".
The Conservatives continued to operate a bipartisan policy "wherever possible", he added.
"But on this bill we are looking at something that would allow people who have committed barbaric murders, things like the Enniskillen Poppy Day massacre, to go free without serving one day in prison or even appearing themselves in court," Mr Lidington told BBC Radio 4's Today programme.
"It was not in the original Belfast Agreement, it is opposed not just by Conservatives, but by Liberal Democrats, by both Unionist parties and nationalist parties like the SDLP in Northern Ireland."
Mr Hain was choosing "very weak ground on which to try to pick a major fight", he added.