A council has said it is "shocked and horrified" by footage of binmen mixing separated recycling waste.
A video posted online shows a Serco worker dumping sorted recycling into one wheelie bin in Whitstable, Kent.
It comes after Canterbury City Council launched a £1m recycling system, with residents encouraged to separate their rubbish into new bins.
Contractor Serco said it was investigating, and that the three binmen may face disciplinary action.
Colin Carmichael, the council's chief executive, said: "A lot of hard work has gone into preparing the new scheme and residents have been diligently separating their rubbish as we asked.
"To then see this happening is completely unacceptable and we are very sorry."
He said the authority was having "urgent discussions" with Serco to investigate what happened, and "strongly hoped" it was an isolated incident.
"If there is any disciplinary action or retraining of staff required, we will insist that this happens as a priority," he said.
"And clearly we will be looking at what we pay Serco in these circumstances."
Sean Trotter, Serco's lead contract manager for environmental services in Canterbury, said staff had undergone "comprehensive training" in its new collection service, which it began rolling out over the last week.
"Unfortunately earlier this week, three collection staff were seen mixing already separated recycling," he said.
"We are investigating this incident with the individuals involved and will be taking the appropriate action which may include disciplinary measures.
"Serco prides itself on delivering the highest customer service.
"We would like to apologise and reassure residents that this was an isolated incident and we are working to ensure it does not happen again."