The Environment Agency has approved a licence to operate a third incinerator at site near Nottingham city centre.
The incinerator would burn 100,000 tonnes of rubbish a year
The expansion at Waste Recycling Group's Eastcroft incinerator still needs planning approval.
John Beresford from Nottingham Against Incineration and Landfill (NAIL) said the city needs "a more modern plant with lower pollution emissions".
The third furnace would burn an extra 100,000 tonnes of rubbish a year on the Eastcroft site.
WRG said they have already saved four million tonnes of rubbish from going to landfill as well as providing power and heat for the city.
John Beresford, of NAIL, said: "We already have an appalling recycling record and send far too much to the landfill - incineration is not the answer.
"We have poor air quality in Nottingham particularly around the incinerator and more incineration will increase this.
"We are confident the city council will reject this planning application."
An earlier WRG statement said: "The proposed extension would further reduce landfill and continue to allow rubbish left after recycling to be used to generate energy."
The firm said it will work within safety guidelines and a bigger capacity will be beneficial.