A ban on plastic carrier bags has come into force in Kenya, which means that anyone found selling, manufacturing or carrying them could face fines of up to $38,000 or prison sentences of up to four years.
The government says the ban will help protect the environment.
But manufacturers of the bags have argued that 80,000 jobs could be lost.
A court on Friday rejected a challenge to the ban. Kenyans are estimated to use 24 million bags a month.
Several other African countries have outlawed plastic carrier bags, including Rwanda, Mauritania and Eritrea.
Kenya’s ban is seen as one of the toughest in the world, although officials say that for now, ordinary shoppers will be warned and have their bags confiscated.
Piles of waste plastic bags are a common site across Kenya, as in many African countries.
Animals often graze on the rubbish and the United Nations’ Environment Programme says huge amounts of polythene bags are pulled out of livestock in Nairobi’s abattoirs – as many as 20 bags per cow – raising fears of plastic contamination in beef.
Image caption Cows in Kenyan abattoirs are often found with plastic bags in their stomachs
Kenya’s Environment Minister Judy Wakhungu says the plastic bags take between 20 and 1,000 years to biodegrade.
“Plastic bags now constitute the biggest challenge to solid waste management in Kenya. This has become our environmental nightmare that we must defeat by all means,” she told the BBC.