Four Fylde bars – three believed to be in Lytham – failed underage alcohol testing in an operation by the council and police.
The joint investigation saw trading standards teams enter bars and pubs on Friday night with underage drink testers, who attempted to get served by staff.
If a person under the age of 18 is served alcohol without being asked for their identification, the pub or bar concerned could be at risk of enforcement measures, including fines or loss of alcohol licence.
Sgt Caroline Hannon, of Blackpool Police’s licensing department, confirmed four venues failed testing procedures, but could not reveal the names of those bars until the managers and landlords had been interviewed.
She added: “The four premises have not been dealt with.
“We still have to interview managers of the bars and pubs about the operation on Friday evening, but we can confirm the four which failed were in the Fylde area.
“We hope to release more information later this week.”
If a bar or pub is found to have sold alcohol to someone under 18, it can face a maximum fine of £5,000 at a magistrates’ court.
If the same bar or pub is found to have sold alcohol on two or more occasions from the same premises within a three-month period, this offence carries a £20,000 fine, or suspension of licence or a closure order.
Insp Mark Thackeray-Scott, of Fylde police, added: “There was a test purchasing operation on Friday. Four establishments failed.
“Our policy is not to give out the names of bars or pubs until enforcement action is decided. These operations are an important part of our licensing operation. We always need to be vigilant and make these checks.”
On Saturday, officers from Fylde Council also enforced outdoor drinking regulations, with some bars and pubs forced to move people inside.