The State Opposition will stop the $440 million Perth foreshore redevelopment mid-construction to retain Riverside Drive if it wins the next election.
Stepping up its attack, Labor has also called for a parliamentary inquiry into the waterfront project.
Amid renewed public debate, Perth MLA John Hyde, whose electorate includes the 10ha site, said yesterday that "voters will have a clear choice".
"We believe that we need something that is certainly not as bulky that keeps Riverside Drive open," he said. "If there are no binding contracts, a Labor government in March 2013 will keep Riverside Drive open."
Major works to carve out a river inlet and build the surrounding development are due to start next month, with Riverside Drive to be rerouted from around May next year.
Asked if a Labor government would halt work mid-construction, Mr Hyde suggested the Government's track record meant "it's a fair bet that a lot of work may not have been done on the Esplanade by then".
When pressed on the issue, Mr Hyde said "clearly" Labor would go back to the drawing board.
"If the Liberals have only wasted $100 million on minor works projects then an incoming government would have to look very, very closely at 'well, let's save $340 million by not continuing on with this bad project'," he said.
Lobby group the City Gatekeepers will today present a 5000-signature petition opposing the project to Mr Hyde and Labor Upper House MP Kate Doust on the front steps of Parliament House.
Planning Minister John Day said Mr Hyde's comments were "fairly silly" and "meaningless".
"Work will be well under way by the election, there will be substantial costs in breaking the construction contract and also in rectifying the substantial work that will have already been undertaken," he said.
Mr Day said Mr Hyde was "captive to the naysayers" and it was this attitude that explained "why nothing has happened over 20 years".