Brighton and Hove Greens have called on the council and waste contractor Veolia to be open about how much cardboard is being burnt instead of recycled.
The party said that Brighton and Hove City Council should not just placidly accept assurances from Veolia.
The Greens said: “News that cardboard meant for recycling may have been sent to the incinerator by the company in charge, Veolia, is scandalous if true.
“Residents in this city pay the council a considerable amount every month to have their refuse collected and many residents spend time sorting their rubbish to ensure as much of it as possible is recycled.
“If they now learn that the people they rely on to process that recycling are simply burning it because they don’t have the staff needed to do the job properly, they are entitled to be furious.
“Both Veolia and the council need to be open about what is going on.
“The council’s statement, which placidly accepts Veolia’s ‘assurances’, will put no one’s mind at rest.
“Local Labour are once again failing to get even the basics right.
“The city is becoming dirty and run down and recycling rates are still in the doldrums.
“Let’s not forget, it was Labour who landed the city with this regressive 25-year waste PFI (private finance initiative) deal in the first place, a deal which pays us not to recycle effectively or even to reduce our waste.
“The Tories then extended the agony for another five years.
“Neither party can be trusted on this issue.
“If the investigation finds a breach of contract has occurred, the Labour group must commit to serious review of the terms of the contract.
“Residents deserve better.”