The party says it fears a programme for government's 'inherent vagueness' will see it fall short
The SDLP is quitting the power-sharing administration at Stormont to form part of a newly established opposition.
The decision comes a week after the Ulster Unionist Party made a similar move.
The Alliance Party has indicated it might not take-up the executive's contentious justice ministry.
It all means the new government could be made up of just the DUP and Sinn Féin.
SDLP Party Leader Colum Eastwood said: "After a long two weeks, despite our best efforts, it has become clear that our ambition for a full Programme for Government will not be matched by the document currently constructed by the DUP and Sinn Féin. We fear that its inherent vagueness will fall far short of what is required.
"The SDLP will be an unrelenting force in the life of the next Assembly, protecting the interests of those who delivered that power and tirelessly holding those who wield it to account," he added.