Sinn Fein delegates have voted in favour of an electoral strategy motion to repeal the Offences Against the State Act as a pre-condition before any coalition talks.
This decision effectively ties the hands of the party leadership in advance of next year's General Election.
The 1939 Act led to the establishment of the non-jury Special Criminal Court which tries terrorist cases.
Dublin South-West TD Sean Crowe earlier urged the party not to limit its options in advance of the general election.
He said: "I do not know if government is ready for me, but I am ready for government."
The party's chief negotiator Martin McGuinness drew laughter from delegates when he remarked that he had experience of coalition government, and with unionists.
But he warned that voters would make the decision whether the party entered government or not.
He said: "I don't think we can afford to be presumptuous. The people who will decide the next election with be the electorate."
Introducing the motions on electoral strategy, vice president Pat Doherty said earlier that the party must focus on securing the biggest possible mandate from the public.
"The issue of coalition in the 26 counties will never arise if we do not substantially increase our mandate and our representation. That is the real politick.
"Our policies will never see the light of day if we do not all leave this hall an deliver the best possible electoral performance in the next Leinster House election."
A local cumann speaker said earlier: "We need to put Fianna Fail out to grass for a couple of years. They have taken the brown envelope. Under no circumstances should we go into government to prop up Fianna Fail after the next election."
PA