Supermarket giant Coles told staff it would keep giving away reusable plastic bags - sparking an angry backlash from environmentalists and a hasty backflip - so it could get shoppers through checkouts quicker during its popular Little Shop toy giveaway.

Coles removed thin, single-use plastic bags from its checkouts nationwide at the start of July, but for several weeks decided to give its thicker 15¢ reusable bags away for free as customers got used to the change.

Facing complaints from some customers, Coles on Wednesday said it would keep giving its "Better Bags" away for free in eastern states and Western Australia until further notice, and would only start charging once shoppers got used to bringing their own bags.

Environmental groups blasted the decision, saying free bags removed any incentive for customers to reuse or bring their own bags, and a day later Coles backpedalled on its decision, saying it would end the free bag offer on August 29.