Charging for plastic shopping bags has again been criticised by a retail body, which says new figures show the numbers used in Wales has fallen by half in the past four years.
Shoppers in Wales will have to pay the 7p charge from next spring.
The British Retail Consortium said educating customers, not penalising them, is the best way forward.
Environment Minister Jane Davidson said charging was essential "to make a difference to the number of bags used".
The Welsh Assembly Government announced in June that they were to introduce the mandatory charge for single use bags, the first UK nation to do so.
The latest figures on bag use among seven supermarkets have been independently monitored by WRAP (Waste & Resource Action Programme).
The British Retail Consortium (BRC) said the number of carriers used in Wales fell from 53 tonnes to 26.6 tonnes in the year to May 2010.
It said the drop was "significantly better" than the average of 45% for the whole UK.
BRC said it shared the assembly government's aim of reducing bag use but introducing a charge would hit the worst off the hardest.
It said Wales also had the best record in the UK in reducing the weight of material used.
Stephen Robertson, the BRC director general, said goods sold in Wales by participating retailers grew by more than 5% between 2006 and 2009.
"Achieving the best reduction in bag use of all the UK nations shows what the voluntary approach can achieve when combined with the high profile given to the issue by the Welsh Assembly Government.
He added: "Despite the continued improvement, we're disappointed the Welsh Assembly Government is still pushing ahead with introducing a bag charge - the first country in the UK to impose these extra costs on shoppers.
"It's particularly bad news at a time when people are already watching the pennies and a move that will hit low-income families especially."
But Ms Davidson said: "Carrier bags are an environmental menace.
"We know that altogether last year we used more than 400m bags in Wales alone, with most of those ending up littering our countryside or rotting in landfill and releasing harmful greenhouse gasses into the environment.
"Whilst I am pleased that Wales is continuing to make steady progress in reducing its use of bags, there's no doubt that progress in this area is starting to peter out and that we are still using far too many bags per person."
The minister said that proved a voluntary agreement has helped to dramatically reduce the number of bags used but a more formal arrangement is now needed.
"The carrier bag charge will give us the incentive we need to keep improving in this area and I am confident that once the charge is implemented, Wales' performance will increase dramatically.
She also said the fact that Wales is doing better at reducing bag use was because of the efforts of retailers and customers and the discussion, publicity and general momentum gathering before the charge is introduced.