Two shops have taken the step of breathalysing people who want to buy alcohol.
The Spar convenience stores in Cardiff city centre are using the devices to tackle problematic street drinking.
The initiative has seen the stores on Queen Street and St Mary Street use breathalysers to test if people buying alcohol are too drunk, Wales Online reported.
However critics argue that it is making shop assistants an unregulated extension of the police and raises questions about profiling the homeless.
An assistant manager at Spar Express, who did not want to be named, said that the store often saw drunk people come in to buy alcohol and had been using breathalysers for several months.
He said: "A lot of drunk people come in and can't control themselves. So when they come in here, can't speak and are stumbling, we breathalyse them."
The initiative is designed to tackle street drinking
Asked how shop assistants decided who to breathalyse, he said: "We use it when we need to use it. If a drunk person comes in, we'll definitely be using it - especially if they can't control themselves in the shop. They have to know the limit - it's kind of like being the police."
The use of the breathalysers was revealed by South Wales Police as part Operation Ash, a crackdown on begging, street drinking, and anti-social behaviour in Cardiff city centre.
As part of the operation, 40 alcoholic drinks have also been confiscated and 18 people have been arrested for begging, being drunk and disorderly, failing to appear at court and breaching dispersal orders.
Dr Kevin Smith of Cardiff University's School of Social Sciences questioned the use of the breathalysers.
He said: "I appreciate and understand a barman at a pub cutting somebody off. But in Spar, particularly in regards to rough sleepers - it's a bit strange because it's an extension of police behavior - a form of surveillance.
"How are they going to decide who gets breathalysed and who doesn't?
"They're not enforcers, they're customer service workers."
The Spar assistant manager said the people they breathalyse are "usually regulars".
"I'll tell them straight - you need to get breathalysed, otherwise we're not going to serve you. They know anyway - they're not stupid. If they're drunk, they know they're going to get breathalyzed." he said.
In a statement on Operation Ash, South Wales Police said it was also working with businesses offering them advice and support on the sale of alcohol.