Environment Minister John Griffiths says the Welsh government "means business" on the carrier bag levy.
He said shopkeepers who do not comply will be fined, although a lighter touch will be taken with enforcement in the first three months.
Shoppers in Wales will be charged at least 5p for single use bags from 1 October. It is the first UK nation to introduce the charge.
But there are claims confusion surrounds the levy.
The Federation of Small Businesses said said some shops were still baffled, but environmental groups said Wales was leading the way on reducing litter.
The Welsh government wants to cut down on the "excessive" number of bags.
All shops, from food stores to fashion retailers, will be required by law to introduce the levy, which it is hoped will encourage people to take their own bags shopping.
The Welsh government wants to follow Ireland's example with a 90% reduction in carrier bag use.
First Minister Carwyn Jones said: "The introduction of our carrier bag charge demonstrates that Wales is a country that genuinely cares about protecting its environment.
"The Welsh public have always been very supportive of the introduction of this charge and I look forward to the dramatic reduction in unnecessary waste that it will bring."
Mr Griffiths told BBC Radio Wales: "We mean business from Day 1 because we expect people to remember their reusable bags right from the very beginning of the charge.
"There are civil penalties and they can run into hundreds of pounds and beyond, but it's not about fining retailers, it's about changing the way people behave and having less of a throwaway society.
"We are quite clear that it will take some time for the change to bed in and that's why we've said that for the three months following 1 October, there will be a very light touch in terms of enforcement because everybody needs to get used to the new position."
Environmental groups, including Keep Wales Tidy and Waste Awareness Wales, have welcomed the charge, saying Wales is leading the way over the issue.
But the Federation of Small Businesses (FSB) Wales has raised concerns that some retailers are still unaware of the impending charges, despite the Welsh government sending out information packs.
It added that other shops had said they were confused about exemptions to the levy and how the fee would be enforced.
"There's a lot of confusion and I think it will take a long time for people to get used to the charge - both businesses and shoppers," said Non Rhys, Wales policy manager at FSB, which has around 10,000 members in Wales.
"Not all retail businesses will have had the packs from the Welsh government because there's not a list of all the retailers in Wales, so we have been trying to contact as many businesses as possible. But there will be some small businesses that do not know."
Leighton Jenkins, from CBI Wales, said it was not the time to impose additional regulation on Welsh businesses.
"We're concerned that these changes will cause confusion at the tills as consumers and retail staff struggle to interpret these complex and far reaching regulations.
"Fast-food restaurants and clothes stores are at a higher risk of facing such consumer confusion due to false public perceptions that the levy only applies to supermarket plastic bags when in fact it applies to all types of bags in all types of shops.
"Retailers have already been forced previously to retrain staff and change processes based on draft official guidance, now they will have to do this again due to the Welsh Government's failure to issue the final guidance until 27 September, just four days before the levy starts."
The British Retail Consortium, which represents all retailers, said its members were ready but that the Welsh Government still needed to "iron out potentially confusing anomalies" over the levy.
"It needs to explain and address anomalies which mean that, for example, you can have a free bag with a carton of chips but not if it comes with a burger in a box," said Bob Gordon, head of environment.
"Or a DIY shop can give you a bag for 500 screws but not for five or six."
Steven Madeley, centre director for St David's shopping centre in Cardiff, said the biggest challenge was making consumers aware of the change.
He said: "It will undoubtedly be a surprise for some shoppers when they are at the tills from Saturday but we need to do everything we can to communicate the message as this will be a big change to shopping culture and to the mindset of consumers."
Firms could face penalties of up to £5,000 if they give away single use bags made from plastic, paper or biodegradable material for free.
Local authorities will have to enforce the levy, although the Welsh Local Government Association (WLGA), said it was unlikely to be "top of the list of priorities" for trading standards and environmental officers.
Businesses with over 10 staff will be obliged to keep a record of the number of bags issued and account for how the proceeds from the charge are used.
Firms are being encouraged to give any profits to charitable and environmental causes.
A spokesman for the Welsh Government said it had been "proactively communicating" with businesses to raise awareness and had sent out two separate information packs in March and August.
"We want to see shoppers avoiding the charge wherever possible by re-using their own bags," he said.
"We expect to see a 90% reduction in bag use once the charge comes into force."
Ministers in England, Scotland and Northern Ireland are also considering measures to reduce the use of carrier bags.
Prime Minister David Cameron has warned supermarkets that unless stores deliver "significant" reductions of the use of single-use bags over the next 12 months, they could either be banned outright from giving them away or be legally required to charge customers for them.