The Office of the Data Protection Commissioner has contacted Dublin City Council in relation to an anti-litter initiative featuring CCTV stills of people who appear to be littering.
The council erected a poster in the Five Lamps area of the north inner city last Friday as part of a new campaign to deter people from littering.
But legal experts have warned that the poster may be in breach of data protection legislation because some of those featured in it may be identifiable.
The Office of the Data Protection Commissioner has said it has advised the council that the processing of personal data must be done fairly and proportionally and must not be overly prejudicial to a person's right to privacy.
Eileen Gleeson, assistant area manager with Dublin City Council, said she believed the poster is not in breach of legislation, and is a proportionate response to illegal dumping.
Ms Gleeson said the poster has been so successful in deterring littering that the council hopes to extend the scheme across the city.
Dublin City Council has said it collects more than 16,000 tonnes of litter each year, and has an annual budget of €25 million for tackling the problem.
The majority of the complaints it receives about litter are in relation to illegal dumping.