Heathcote MP Lee Evans says motorists should "demand as the only option" a four-lane bridge on Heathcote Road over Woronora River at Engadine.
Mr Evans made the comment after an outcry followed the Leader's online report last Thursday that the bridge would be closed for six months at the end of 2021 so the lanes, shoulders and approaches could be widened.
The state government has rejected calls to duplicate the narrow bridge, which has been the scene of many accidents over the years.
There will continue to be just one lane in each direction on the bridge, which was built by the military in 1943.
"People, my preferred option is and has always been 4 lanes. What I need you all to do is demand that as the only option," Mr Evans posted on the Leader Facebook page.
"I have been fighting for 4 lanes since 2015. I need you to make sure you go to the consultation site and fill it in demanding 4 lanes."
Mr Evans was more moderate in a later statement, saying, "With initial planning completed last year, I am pleased the process to get this done is moving ahead to make the bridge safe.
"However, I strongly state that this is not my preferred option and I will continue to fight for a four lane bridge.
"It's extremely important that the community participates in the community consultation to express their views for the bridge upgrade. "
A spokeswoman for Transport for NSW said widening the existing narrow lanes to standard lane and shoulder widths would significantly improve safety for motorists, especially larger vehicles.