Tesco has been fined £6,000 after repeatedly selling alcohol to under-age youngsters.
Britain's biggest supermarket chain is believed to be the first retailer in the country to be prosecuted under a "three strikes and you're out" rule.
Tesco admitted "persistently selling alcohol to a child or children" between October 9 and November 3 last year at Blackpool Magistrates' Court.
The prosecution was brought by Blackpool Council.
A council spokeswoman said: "New powers under the Licensing Act mean that if a premises is caught three times in three months serving someone under the age of 18 they could be eligible for a fine or prosecution."
A sting operation was carried out at a Tesco Express store on Ansdell Road in Marton, Blackpool, where 16-year-old test purchasers were able to buy alcohol.
A council spokeswoman said they targeted the store after receiving complaints about alcohol related disorder in the area.
The store was fined £6,000 and ordered to pay £250 costs. The shop's licence was suspended for 28 days, but this has been put on hold while the store appeals.
A Tesco spokesman said: "We take our responsibilities towards the sale of alcohol very seriously.
"To support our staff in preventing underage sales, stores will be moving to a Think 25 policy. This means that if a customer looks under 25 and does not have appropriate ID, they will not be sold alcohol in our stores."
