Kaipara police are warning bars to check properly for underage boozers after two were nabbed selling alcohol to under-18s in an undercover sting.
In a covert exercise by police and the Northland District Health Board, minors attempted to buy booze at four bars or pubs, two of which served them.
Kaipara police alcohol harm reduction officer Sergeant Howard Clement said the latest result was disappointing.
"[It] has shown lax systems and considerable improvement is required.
"All licensees and their staff should assess the age of anyone who appears under the age of 25 by insisting on a form of photo identification. No photo identification, no sale, it is that simple."
Four off-licence premises were also targeted, but none served the minors.
Police have been running similar stings in Northland for almost 10 years.
The bars that failed may have their alcohol licences suspended or cancelled.