Staff at Anthology on Swan Street say the problem has been exacerbated following the closure of the Revolution Bar on Alderley Road.
Now, no-one under the age of 21 will be allowed in the pub after 9pm on Friday and Saturday.
READ > Wilmslow fitness coach celebrates special milestone
Everyone must show ID.
The bar says it has been forced to take action to maintain its license.
Posting on social media, a spokesman for Anthology, said: “This decision has not been taken lightly and will be reviewed over time.
“We’ve never had a problem serving under 21s, but since Rev has closed, we’ve had a huge influx of people under 21, with numbers increasing every week.
“Unfortunately, this has brought a number of under 21s smuggling their own alcohol in, sneaking their underage friends in and buying them drinks.
Revolution Bar on Alderley Road has closed (Image: Google Maps)
“There’s a total lack of respect for other customers and our staff which we will not tolerate.
“We’d like to be clear. This is not all our under 21 customers, but a large bulk of the influx we have received since Revs has closed.
“We apologise for any upset this may have caused but we have to think about our license.”
Staff say underage drinkers have been refused service at the bar and asked to leave due to no ID.
However, some people have given their underage friends their own ID so they can drink in the pub.
Revolution Bar in Wilmslow was one of eight venues closed by the nationwide chain after the company warned that its younger customers are still feeling a ‘disproportionate’ strain from rapid increases in the cost of living.
