This week, environment minister Jane Davidson said she wanted to ban free bags by as early as 2010 to reduce litter and limit damage to the environment. She cited the experience of the Republic of Ireland, which cut bag usage by 90% when it introduced a charge in 2002.
Asda said it was "firmly against charging because it would impact disproportionately more on families on low incomes who shop on a budget".
Charges were unfair, added a Sainsbury's spokesman. "We believe in working with customers to bring about lasting behavioural change, rather than penalising them for using carrier bags," he said. "Over the past two years, we have been working with customers to drive down bag usage and the environmental impact of our carrier bags has been reduced by 63%."
Retailers had already cut bag usage by 50% and it was wrong to interfere with individual companies' policies, the BRC said.
The Welsh Assembly said it was seeking views from the industry and the public on how much to charge, which bags to include and how the scheme should be enforced.