A raucous convoy of cars took to the Princes Highway in Wollongong on Saturday to protest against the expansion of the Russell Vale mine.
It is the third formal protest against the expansion in a month.
Dozens of environmental activists from the Illawarra Climate Justice Alliance and Protect Our Water Alliance met in the Vikings Rugby Club car park at 11am before forming a car and bicycle convoy along the Princes Highway.
"We wanted a way to make our message heard and stay COVID-safe," organiser Kaia Morgan said.
"We've seen the only way decision-makers will listen to us is if we protest."
Wollongong Coal gained approval for its mine extension at Russell Vale in December last year, capping off a more than decade-long effort by the company.
Wollongong Coal plans to extract 3.7 million tonnes of coal from under the Greater Sydney water catchment over the next five years.
Opponents say the expansion poses a risk to the drinking water supply of more than five million NSW residents, and that it will contribute an extra 11 million tonnes of greenhouse gas emissions.
Another organiser, Jack Mansell, said the group believes Australia has the capacity to transition to clean energy without workers losing out.
"What we need is obvious - a rapid transition away from fossil fuels," he said.
"We believe we have the resources and the human capacity to solve the problems we face."
Last week, protesters from Stop Russell Vale Mine spent about an hour blocking the path of arriving and departing vehicles, in an action aimed at interrupting Wollongong Coal's expansion preparations.