Supermarkets have been covering up non-essential goods as Wales enters a national lockdown.
From 18:00 BST shops will be forced to close for 17 days, unless they sell essential items such as food.
First Minister Mark Drakeford has said supermarkets should also stop selling items such as clothes as a matter of “fairness” until 9 November.
But the Welsh Retail Consortium said it was “deeply disappointed” with the “ill-conceived policy”.
Retailers have said the rules are confusing as they have not been given any definition of what is essential.
By law, clothing and homeware stores, and garden centres, will have to close during the national lockdown, while supermarkets, pharmacies and hardware stores can remain open.
On Thursday, the Welsh Government said that supermarkets would be told not to sell non-essential goods, like clothes, toys, decorations and electrical items during the 17-day firebreak.
Plastic covering was seen placed over pillows and cat baskets in Asda in Coryton, Cardiff.
The company said it had been given “little time to implement these changes or clarity on what is deemed ‘essential'” and had “expressed our deep concerns about the implications for customers accessing products they genuinely need”.
Tesco said it would work “incredibly hard” to comply with the Welsh Government’s rules, while Sainsbury’s said it was “working around the clock to put changes in place”.
The Welsh Retail Consortium said: “In spite of the dearth of government clarity, our members’ focus now will be on equipping hard-working colleagues with as much information as possible given the undoubted uncertainty and complexity that has been caused by this decision.”
Guidance published for retailers on the Welsh Government’s website says aisles selling homeware and decorations, toys, mobile phones, clothes and games, should be “closed to the public”, and some areas may need to be cordoned off.
Speaking at Friday’s Welsh Government briefing, Mr Drakeford said the decision to stop supermarkets from selling all but essential items was based on a “need for fair play”.
“I’m not prepared to treat small businesses in Wales in one way, requiring them to close – they are not able to earn a living during these two weeks, as part of our national efforts – and then simply because another sector in society are more powerful, are bigger, that they think that they can be treated differently.
“It is a straightforward matter of fairness, we are in this together here in Wales.
“No individual and no organisation is above the effort that we are all required to make.”
Mr Drakeford said “many hundreds” of small businesses would be closed across Wales.
“We cannot do that and then allow supermarkets to sell goods that those people are unable to sell,” he said.
He added: “This is not a period to be browsing around supermarkets looking for non-essential goods.”
The Welsh Conservatives have said businesses and the economy would be hit “very, very hard” by the rule, and Plaid Cymru said communication about what the rule meant was “lacking”.
Mr Drakeford defended himself from criticism of the plans saying they were making decisions under “huge pressure.”
“We said from the very beginning that non-essential retail would close in Wales,” he said. “All we are doing is clarifying that and remaining consistent with that initial decision.”
If people could not find essential products in supermarkets there were ways around the problem, he said, adding that friends and neighbours were “often very willing to help”.
“There are online ways that people can purchase goods,” Mr Drakeford said. “It is not a problem without a solution.”
Senedd Conservative leader Paul Davies said: “It shouldn’t have come to this in the first place.
“We believe that introducing this temporary national lockdown is disproportionate and will actually hit businesses and hit the economy very, very hard, and therefore in our view obviously independent retailers should be allowed to open as well.”
Plaid Cymru health spokesman Rhun ap Iorwerth claimed Welsh Government communication was lacking.
“I think that’s been the story throughout this pandemic,” he said.
“I’ve been arguing on behalf of businesses in my constituency back in May, June, July, give us plans, give us an idea of what is ahead.
“This firebreak needs to be a reset for the way government communicates these messages.”