The Princes Highway at Gerringong will be partially closed until at least Tuesday after cracks were found in a new section of the roadway.
The section is just south of the Belinda Street intersection and affects traffic travelling in both directions.
The northbound lane will remain closed and all traffic will use the southbound lane under a "stop/slow" arrangement until at least Tuesday.
The location created traffic headaches this week after a few days of heavy rain damaged an embankment.
"Damage to the embankment has caused small cracks and rutting to appear on the road surface, reducing safety for motorists," Kiama MP Gareth Ward said.
Geotechnical work to stabilise the road had not been completed when the heavy rain came, Mr Ward said.
"The stability of the embankment has been assessed by geotechnical engineers and the condition of the road surface is being monitored by surveyors."
Extra work has already been completed to stabilise the bottom of the embankment with rock fill.
Roads and Maritime Services had liaised with the Environment Protection Authority to allow work to be carried out around the clock to fix the problem as quickly as possible.
"The changed traffic conditions are expected to be in place until at least Tuesday, August 26, weather permitting, while work to build the new road surface is carried out," Mr Ward said.
"When complete, the highway will reopen to two lanes."