People in Lichfield and Burntwood are being warned not to put items that cannot be recycled into their blue bins after five truck-loads were turned away from a sorting plant.
Lichfield District Council says it has stepped up checks for items such as black bin liners, unwashed recycling and used nappies after they were found during checks.
The local authority is now putting stickers on bins to remind residents – and said it will not empty any with contaminated waste.
Councillor David Leytham, Cabinet member for operational services, leisure and waste, said: “Our aim is to send as much of your waste to be recycled as possible.
“If loads of our recycling are turned away, it costs us money and is really disappointing as we know the majority of our residents work hard to recycle.
“We now need everyone to make sure they follow our guidance, which includes only putting recyclable items into your blue bins, making sure dirty items are rinsed out, and not putting recycling into black bin bags.
“By following these instructions, you won’t find a note on your bin saying that we cannot empty it due to contamination.”
Advice on what goes in which bin is available online.