Sutherland Shire Council has condemned the state government's go-ahead of mining under Woronora Dam and called for the decision to be reversed.
Councillors said the dam provided much of Sutherland Shire's drinking water, which would be at risk if mining proceeded.
A motion, which received unanimous support at the April 27 meeting, will also see a request to state planning officials to address the council to explain the decision making.
The Department of Planning, Industry and Environment gave final approval for the two mines under the reservoir despite protests by more than a dozen environmental and community groups and a hard copy petition signed by 10,700 people.
The council meeting heard approval was given in 2009 by the Labor government, with the present government signing off on the previously set conditions and details of extraction.
Some councillors were sceptical another council resolution would carry any weight given a similar resolution in late 2019 failed to sway the government.
Cr Michael Forshaw (Labor), a former senator, said it was not too late for the decision to be reversed.
"There is a power with the state government to override this decision," he said.
"The problem is they would have to pay compensation.
"But, it wouldn't be the first time a project has been stopped and compensation paid out."
Liberal Kent Johns said the Keneally Labor government made the original decision and the present minister couldn't be blamed.
Labor councillors said more recent environmental studies provided sufficient cause to reverse the approval.
Cr Diedree Steinwall (Labor) said a 2014 report by the Chief Scientist said NSW was alone in permitting long wall mining under precious drinking water.
Deputy mayor Steve Simpson (Independent) said, apart from one previous issue, he had never received more protests from residents.