New 5p rule comes into force across the country.
Wales has become the first UK nation to introduce a levy on single-use carrier bags.
Customers must now pay a minimum of 5p per bag as part of a new law designed to cut back on their excessive use.
Retailers which don’t comply with the ruling face fines of up to £5,000, although businesses are expected to have three months to get used to the ruling before it is rigorously enforced.
The British Retail Consortium (BRC) said last week that its members were ready to begin charging for carrier bags but has warned that it needs to be made clear to shoppers that the extra cost is being imposed by the Welsh Government.
It has also called on the government to iron out some potential grey areas around the rule.
“The best way for customers to avoid cost and confusion is to remember to take their own bags to stores,” said Bob Gordon head of environment at the BRC.
It is thought that the carrier bag tax could raise more than £2.5m in its first year, which will be given to Welsh charities.
There are certain exemptions to the bag levy, mainly for unwrapped food items.