Campaigners against a proposed waste plant at Nine Mile Point Industrial Estate have handed in around 700 formal letters of complaint to Natural Resources Wales.
Residents from Cwmfelinfach and Wattsville want NRW to refuse an operating licence.
The plant, being developed by Hazrem Environmental Ltd, will process up to 100,000 tonnes of waste annually and residents from the two villages argue it will have a detrimental impact on the environment. They cited an increase in traffic and a weather phenomenon called temperature inversion as reasons for objection.
Planning permission for the building was approved last year by Caerphilly County Borough Council.
Islwyn AM Rhianon Passmore joined campaigners as they handed in their objections.
She said: “I am strongly calling on National Resources Wales to deny this permit, use its teeth and adjudicate on the sides of the communities it is meant to safeguard.”
Jon Goldsworthy, Operations manager for Natural Resources Wales, said it was satisfied there would be no detriment to the environment or harm to human health.
He added: “Continuing the process, we are now consulting local people on the draft permit, inviting them to provide us with any information which has not come to light to date that we should consider.”