The Berejiklian government was left flat-footed on the issue on Friday afternoon, as Woolworths, Coles, and Harris Farm introduced their owns plans to stop supplying plastic bags to customers in a bid to tackle the huge environmental cost from the product. 

Environment Minister Gabrielle Upton welcomed the move by the retailers, but declined to say whether the NSW government would now endorse the measures through a statewide ban.

Opposition Leader Luke Foley seized the opportunity to wedge the government on the issue, describing a statewide ban as a "simple no-brainer" and offering to work with the government to implement one. 

"What we have is these major retailers committing to banning single-use plastic bags but not a peep from the NSW government on whether they will implement a statewide ban," he said.

"If Coles and Woolworths can join forces then the Liberal and Labor parties can."

Harris Farm chief executive Angus Harris said the market-driven ban was encouraging, but the NSW government now needed to "cement" it through regulation.

"We are well and truly years behind," he said. "We're even behind countries like Kenya, which brought in a plastic bag ban last year."

South Australia, ACT, the Northern Territory and Tasmania have already implemented statewide bans, while there are plans in place for Queensland to do the same next year.

Mr Harris said the issue had been "top of mind" in the retail industry, which was why Coles and Harris Farm were able to announce their own bans within hours of Woolworths leading the way with its shock announcement on Friday. 

"The first thing we did was call our [plastic bag] supplier and say we want to stop," Mr Harris said.

The two supermarket giants committed to phasing out single-use plastic bags in NSW stores by June 30 next year and will instead make reusable plastic bags available for purchase at the checkout.

Harris Farm went a step further. The stores will cease all supply of plastic bags from its checkouts from January 1 next year. Instead, small single-use paper bags and cardboard boxes will be available for free, while reusable paper bags will be sold at 15 cents or cost price, whichever proves cheaper.

"We're definitely expecting push-back from customers," Mr Harris said. "The last thing we want to do is making shopping more expensive."

"But I think our customers can see that this is the way the world is moving. And the way it has to move."

Since April, Harris Farm has reduced its annual supply of 22 million single-use plastic by 35 per cent by encouraging customers to purchase the reusable paper bags.