Mr Robertson visited the banks of the Nepean River at Menangle with Macquarie Fields MP Andrew McDonald two weeks ago and said the government should suspend all coal seam gas exploration licences until its affect on nearby waterways and aquifers were fully understood.

His comments drew criticism from Liberal MPs who slammed the previous Labor government for issuing the licences in the first place.

"In the case of the Camden Gas Project, which straddles the Nepean River, the government should reject any proposals from AGL to expand its operations outright," Mr Robertson said.

"Evidence from overseas and interstate indicates that coal seam gas mining operations could have a devastating and permanent impact on groundwater resources.

"Until there is a scientific consensus that coal seam gas won't damage water catchments in places like Sydney's south-west, we need to hit the pause button."

Dr McDonald said local farmers and residents had raised concerns about the coal seam gas mining under way in the Macarthur region.

"South-west Sydney has become somewhat of a guinea pig for the coal seam gas industry," Dr McDonald said.

"But at what cost to the local community?"

Dr McDonald said a precautionary approach was needed.

Wollondilly MP Jai Rowell said Mr Robertson had the opportunity to rally against the issuing of coal seam gas extraction licenses when he was in government.

"I find it highly hypocritical that someone as experienced as John Robertson would come out and say that when his government, of which was a senior cabinet minister, was the one who issued those exploration licences.

"There is a moratorium on new licences and this government hasn't issued one single licence since March 26 when we were elected."

An upper house inquiry into coal seam gas extraction is currently under way and the O'Farrell government has banned the use of fracking and BTEX chemicals until the end of the year.