A plastic bag tax could hit small businesses in Northern Ireland and the most vulnerable who can least afford it, a member of the Environment Minister's own party has said.
DUP minister Edwin Poots insisted the levy would encourage more sensible use of a "virgin resource".
But Strangford MLA Jonathan Bell said there were real misgivings over the plans.
He warned of the "impact a plastic bag tax will have, particularly on small family businesses and on people who are vulnerable and who cannot afford it, and ultimately a tax that may not even protect the environment".
The tax could be 15p per bag. At present millions are used for groceries in supermarkets and at other shops.
In the Republic of Ireland the levy was introduced in March 2002 at the rate of 15 cent per bag. Its primary purpose was to reduce the consumption of disposable plastic bags by influencing consumer behaviour, with proceeds put into an Environment Fund.
According to the Republic's Environment Department it had an immediate effect on consumer behaviour, with a decrease in plastic bag usage from an estimated 328 bags per capita to 21 bags per capita overnight. Shoppers were encouraged to use tougher, reusable bags.
Mr Poots said: "The funding that you raise will be put back into environmental projects which will actually deliver the potential for people living in fuel poverty in Strangford and elsewhere to come out of fuel poverty. I think that is something which is worthwhile, that is something which is good.
"We do have to get to the point where we are better using our resources as opposed to always using a virgin source of material and then throwing it away.
"Those days are gone. We are changing to a better environmental practice and one of those better environmental practices is to use reusable bags."