A health study on opencast mining at Margam says it is badly affecting the well-being of people living nearby.
Celtic Energy wants to extend mining at the site between Port Talbot and Bridgend for 10 years, but opponents hope planners will turn it down.
The report said that while ill-health could not be directly linked to the site, there was "sufficient uncertainty" to justify refusal.
Celtic Energy has been asked to comment but has so far not responded.
The health impact assessment was carried out by Cardiff University's Welsh Health Impact Assessment Support Unit - a body supported by the Welsh Assembly Government and the National Public Health Service.
The unit promotes the use of and understanding of health impact assessments for planning and other purposes by local authorities, voluntary agencies and other groups.
Stress related illness
It was approached by residents and asked to examine the impact of the proposed extension on the communities most affected by the plan to extend opencast mining - Cefn Cribwr and Kenfig Hill in the Bridgend area and Aberbaiden, Bryndu and Pen y Bryn on the Port Talbot side.
The authors drew upon published research and monitoring data, but a lot of the work was based on feedback from six focus groups with people living in the area.
Mining at Margam is currently set to end in 2007. Celtic Energy, which told the report authors that the mine employs 65, wants to extend it westward with the aim of extracting a further 2.4m tonnes of coal.
"I think it's a powerful report and the conclusion definitely comes out in our favour"
The report said residents raised many different health concerns with respiratory, cardiovascular and stress related illness mentioned most frequently.
It said emissions from the current site complied with present guidelines, but these were being reviewed.
It was not possible to present evidence of ill-health in adults that could be directly attributed to Margam.
But it said residents presented evidence that asthma in children was more prevalent closer to the present mine and this finding was supported by the public health literature.
It concluded there was strong evidence "regarding the negative impact on general well being" of living near the mine.
"Data from the focus groups showing the distress this is causing indicates that there are profound impacts on psychological wellbeing.
Blasting
"On balance, there is sufficient uncertainty regarding the negative health impacts to apply the 'precautionary principle approach' - which would not allow mining to proceed in such close proximity to residential areas."
Copies of the report have been forwarded to both Neath Port Talbot and Bridgend councils. They have no statutory obligation to take the report into account when looking at the application but campaigners hope it will influence the decision.
Gaynor Ball of the campaign group Pact said: "I think it's a powerful report and the conclusion definitely comes out in our favour.
"If you complain about the dust, the noise or the blasting we are told it's all within the limits of the law.
"But we know we are suffering. We are just fed-up as a community."
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