Police and council chiefs in Swansea plan to fine anyone who lends their ID to under-18s to buy alcohol.
The youngsters could also be arrested on suspicion of thieving the ID.
It follows the seizure of 356 IDs — many owned by siblings — from teenagers trying to enter the city's pubs and clubs in the past three and a half months.
Community safety sergeant Dean Evans said: "It has come to our attention that this is an increasing problem.
"To combat the problem and deter licence and passport holders from letting others use their ID fraudulently, we are looking to introduce a fine system whereby the legitimate owners of a seized ID will be fined when they retrieve their ID from the police.
"We are very fortunate in Swansea city centre to have vigilant door staff who are spotting many of these frauds and seizing ID.
"We will also arrest individuals suspected of using borrowed ID in a fraudulent manner.
"Parents or guardians will have to accompany the person at a police station for questioning."
The level of fines for those who lend ID documents has not yet been decided.
The scheme is being led by the Safer Swansea Partnership, whose evening economy co-ordinator Steve Williams said: "We have given people using fake ID chances, but the problem is still increasing.
"Some are fake IDs, some are stolen, some are tampered with, but a large number of the IDs we are seizing are ones that have been lent to under-18s.
"This will not be tolerated in Swansea and is being taken very seriously by Safer Swansea. We will continue our multi-agency operations in 2010 with the intention of stamping out under-age drinking in city centre venues."
Morning Advertiser legal editor Peter Coulson said: "I'm not sure what legal basis they have to charge somebody who lends ID to someone else. It's a long shot. Why not prosecute the young person [who tries to buy ID]?"