Pubs were found to be selling alcohol to underage teenagers when police sent 15-year-olds undercover.
Three Leeds pubs fell foul of a police test purchasing operation after officers sent the young volunteers into premises to attempt to buy alcohol.
Of 10 pubs targeted by police in the Headingley and Hyde Park areas of Leeds, three sold alcohol to the 15-year-old recruits.
And bar staff faced disciplinary action from their employers after being caught out by the sting operation.
Sgt Dave Shaw, from Leeds District Licensing, said: “The thirty per cent failure rate on this latest operation is completely unacceptable and shows that licensed premises need to be doing more to comply with the law and prevent children from buying alcohol.
“Children and alcohol is a dangerous mix that affects the health of our young people and makes them more vulnerable to crime.
“It also increases anti-social behaviour in our neighbourhoods, and pubs and bars must do more to prevent this.”
Sgt Shaw said pubs faced further test purchasing operations after police previously focussed on off licences.
He said: “Any premises who are found selling to children twice within a three month period risk having their licences removed by the council.”
The staff members who sold alcohol during the operation were dealt with through community resolutions. They were also facing internal disciplinary proceedings, Sgt Shaw added.