Protesters have barricaded the entrance to a £500m incinerator being built near Gloucester.
Construction work has begun at the site off the M5 at junction 12 near Stroud and it is due to operational in 2019.
Protester Jojo Mehta said: "It discourages recycling at every stage, it's incredibly expensive and doesn't save the council in the way it's been described."
Developer Urbaser Balfour Beatty said people had the right to protest.
A spokesman for the company said: "Our main concern is to ensure the health and safety of people in and around the site.
"We respect the rights of people to make legal and peaceful protest."
A dozen people blocked the entrance and a lorry bringing a delivery to the site had to turn back because of the blockade.
Protesters say they aim to be on site for the next 48 hours.
In 2015, Stroud District Council lost a legal challenge in the High Court against the plans on the grounds the planning inspector had "made errors".
In March, a legal complaint was lodged by the charity R4C that the contract awarded to Urbaser Balfour Beatty breached competition laws.