Campaigners opposed to plans to raise Warragamba Dam wall were last week "excluded" from a Water NSW community consultation meeting about the project.
The Water NSW workshop was held at Warragamba Town Hall last Wednesday but some of the region's key stakeholders were left off the invite list.
The workshop focused on the construction process of the proposed wall-raising, prior to the completion of a final environmental impact statement.
Give A Dam campaigner Harry Burkitt said he was appalled that key community members were not invited to the workshop.
"The Warragamba community deserves full consultation about this dam proposal," he said.
"It's an absolute farce for the government to only invite people who agree with its dam proposal.
"It is now incumbent on whatever Federal Government is elected in May to stop this developers' dam."
A draft environmental impact statement (EIS) confirms the sides of the wall will be raised 17 metres to allow for future expansion, putting at risk heritage-listed forest in the Blue Mountains and Burragorang Valley.
Previous documentation from the government stated the wall would only be raised 14 metres.
The EIS statement - which is due to be made public later this year - doesn't assess the impact of raising the wall 17m, meaning a much larger upstream area of the heritage-listed Blue Mountains national park would be inundated with water.
Warragamba local and traditional land owner Kazan Brown, who has criticised plans to raise the wall, was among those excluded from the workshop invite list.
She said it was disappointing to not be invited.
"I am a part of the community as well - they didn't invite any indigenous representatives," Ms Brown said.
"This was the first community consultation about raising the wall and as such it should have been open to the whole community, not just the people on the invite list."
Give A Dam is taking its fight against the project to the United Nations Educational, Scientific and Cultural Organisation (UNESCO) this week. Mr Burkitt hopes the World Heritage Committee will convince the government not to allow destruction of a heritage site.
"If the Australian Federal Government allows the NSW Government to continue down its destructive path of flooding a world heritage site, UNESCO will rightfully come down on Australia like a tonne of bricks," he said.
"The federal government will be asked to decide on the dam proposal in the coming months through federal environmental laws. Federal politicians should be listening to the thousands of Australians opposing this project and rule out supporting the proposal before international bodies step in."
The member delegations of the World Heritage Committee will be fully briefed on the natural and cultural sites that would be destroyed from raising the dam wall.