Next year's European election should be accompanied by a referendum on whether people want the current Assembly term extended by a year.
Deputy leader Dolores Kelly made the call as delegates at the SDLP conference endorsed former Environment Minister Alex Attwood as their candidate for the May poll.
The next Assembly election had been due in 2015 but will not now take place for a further year, to bring Stormont into line with the other devolved administrations in Scotland and Wales.
Mrs Kelly told delegates: "The people of the north gave us a mandate for four years and four years only, and we should not try to extend this mandate without consulting them."
In the opening session as rank-and-file members backed a motion calling for a wider vision on energy policy, the man who replaced Conall McDevitt as South Belfast MLA – former UTV reporter Fearghal McKinney – said: "The north is well placed to harness the potential of tidal and wind energy.
"However, if we are to embrace fully a renewable energy supply, we have to accept that in the short- term this may be a costly vision.
"Significant upgrades to our current transmission and distribution infrastructure are needed. These necessary upgrades will be extremely costly in the short-term but, if carried out, will lead to more affordable, clean and secure energy future."
He called on three departments – Enterprise, Trade and Investment; Environment, and Agriculture and Rural Development – to work together to stimulate the development of renewable energy.