Extinction Rebellion held a protest on Stroud High Street on Saturday ahead of a demonstration at Javelin Park incinerator on Monday morning.
Protestors met and spoke to shoppers as a model incinerator blew smoke from its chimney.
The gathering took place as the incinerator prepared to receive its first deliveries of residual waste on Monday.
ER spokesman David Lambert said, “We will be there at Javelin Park to greet its first deliveries. We will be there to uphold the law, not break the law.
Mr Lambert explained that ER protestors would be preventing the waste disposal vehicles from entering the site.
“We will be there to ask arriving drivers of the garbage vehicles to show us their permits,” he explained.
As far as can be ascertained, ER protestors believe the plant will receive unsorted debris from domestic and commercial rubbish bins.
“The burning of such unsorted material is illegal,” Mr Lambert said.
“If a member of the public has filled his rubbish bin with highly toxic detritus, and it is taken to the incinerator to be burnt, it will release poisonous gas into the atmosphere,” he added.
“Currently, there is no other regulating of what is going into our bins and therefore everything that we throw into our black bins will be incinerated.”
As such, the ER organisation believes that the incinerator is an unlawful operation with its proposed burning of unsorted waste.
“Gloucestershire County Council and Urbaser Balfour Beatty, the operators of the plant, are committing a crime,” Mr Lambert said.
Protestors will be meeting from 8:30am.