Residents in a Welsh city face being fined £100 if they refuse to recycle.
Bin-bag patrols have begun in Swansea as part of an effort to increase recycling rates.
Newly-appointed council officers are checking residents' household waste at the kerbside to ensure black bags do not contain recyclables such as plastics, paper or glass.
The controversial measures, approved by the council in December, could see residents handed fixed penalty fines.
Teams carry out inspections by shaking, but not opening, the black bags to listen for possible recyclable items.
Swansea council's head of waste management, Chris Howell, said the plans were designed to tackle the "minority" of people who still refused to recycle.
"Probably four out of five people recycle really well but it's about getting the one out of five to change their behaviour," he said.
"Welsh Government-led analysis right across the country has shown that half of the materials found in black bags are recyclable, while a quarter of it is food waste."
The council decided not to follow other local authorities such as Conwy council which became the first in Wales to limit bin collections to once a month.
However the scheme has received a mixed reaction from residents, with one calling the scheme an "invasion of privacy".
Welsh councils are under pressure to hit Welsh Government targets on recycling.
Currently 58% of all waste must be recycled but that is set to rise to 64% by the end of April.
Councils falling short face fines of £200 per tonne of excess waste.
But Keep Wales Tidy said the recycling message is still "relatively new" and in some areas there has been confusion about what can be recycled and changes to collections.
"Fair enforcement can play a part but we want to see education before enforcement," said the environmental charity's Amy Lloyd.
"We would like to see all efforts for engagement exhausted before enforcement is carried out."
She called for a "real push" by Welsh Government, councils and charities to raise awareness about what can be recycled.
The Welsh Local Government Association said councils faced "challenging" targets.
A spokesman added: "Local authorities have been very successful in increasing levels of recycling, however every additional percentage becomes harder to achieve.
"Encouraging more residents to make sure they are putting everything possible into recycling collections can therefore help hit targets."