Work to construct a new foot and cycle bridge across the Lagan - first announced five years ago - needs to begin, a cross-party group of MLAs has said.
The Lagan Pedestrian and Cycle Bridge will connect Ormeau Park to the city centre through the Gasworks business park.
Campaigners said it would dramatically improve connectivity from the south east of the city and reduce traffic congestion by making it easier for people to walk and cycle.
Proposals for the bridge were unveiled in 2014, and planning permission was granted in April 2016.
However, MLAs fear the project may not get under way as, under the law, work is required to begin within five years, meaning permission will run out in 2021. Funding for the project was included as part of the Belfast Region City Deal - a 15-year, £350m Government investment package.
In a joint statement, South Belfast MLAs Clare Bailey of the Green Party, Paula Bradshaw (Alliance), Claire Hanna (SDLP) and Mairtin O Muilleoir (Sinn Fein) called for progress.
They said: "Building this bridge would open up the potential for many more people to walk or cycle into the city for work, to shop or for leisure.
"It is the only City Deal-referenced project which has planning permission and should be green-lighted now. This bridge will reduce traffic congestion, air pollution and improve residents' health and wellbeing. It would also connect different parts of the city, boost user numbers in Ormeau Park and encourage more pedestrians and cyclists to use the Lagan towpath."
Ashley Hunter, Northern Ireland director of sustainable transport charity Sustrans, said the bridge had the potential to transform people's commute and air quality in the inner city area.
"Given the serious problems of car congestion in the city, we welcome the cross-party support for this bridge which will have a transformative effect on south Belfast by boosting walking and cycling," he said. "There is no reason why construction work should not begin straight away to complete this project."
The Lagan Bridge could cost between £7m and £9m to build and has already cost nearly £500,000 of public funds to develop the plans.
The Department for Infrastructure has been contacted for comment.