The government has refused to release details of up to 100 "side deals" struck with Democratic Unionists during talks on reviving devolution in 2004.
The government refuses to release details of "side deals"
The SDLP had asked that the details be published under the Freedom of Information Act.
But the government said the information could prejudice the United Kingdom's relationship with the Irish government.
It also warned that it might damage the political process. The SDLP intends to appeal against the refusal.
The SDLP's Sean Farren said on Wednesday that the political process was dealing with the after-effects of the so-called Comprehensive Agreement.
This was the failed 2004 document proposed by the two governments after months of negotiations involving the DUP and Sinn Fein.
The deal collapsed after the IRA refused to give in to DUP demands that its disarmament process should be photographed.
The SDLP requested the information in March, after DUP deputy leader Peter Robinson claimed his party had secured more than 100 secret side deals and understandings during talks on the Comprehensive Agreement, involving the Irish government and Sinn Fein.
"A shadow assembly is now being put in place because this was agreed by the DUP with Sinn Fein in the Comprehensive Agreement," Mr Farren said.
"While the British government say that they are not wedded to the Comprehensive Agreement, (Northern Ireland Secretary) Peter Hain confirmed last week that they are still talking about legislation later this year to implement parts of it before there could be restoration.
"That is why the SDLP wants all the side deals that the DUP has on the Comprehensive Agreement made public - and why we put in the freedom of information request."
Mr Farren said the public had the right to know what changes there might be to the Good Friday Agreement for which they had voted.
If the Comprehensive Agreement had been struck in 2004 and devolution revived, there would have been changes to the way the assembly operated.
These include how the first and deputy first ministers would be elected as well as the entire ministerial team.
Peter Hain said the governments would "not blink" on deadline
Under current proposals, the assembly will be recalled on 15 May with parties being given six weeks to elect an executive.
If that fails, the 108 members get a further 12 weeks in the autumn to try to form a multi-party devolved government. If that attempt fails, salaries will stop.
Mr Hain and Irish foreign minister Dermot Ahern have stated that there is no flexibility in the deadline for restoring devolution.
At a meeting in Dublin in Tuesday, Mr Hain said they would "not be blinking" on the November deadline.
If the attempt fails, the British and Irish governments intend to work on partnership arrangements to implement the Good Friday Agreement.
Devolved government at Stormont was suspended in October 2002 following allegations of a republican spy ring.
A court case arising from the allegations later collapsed.