Dublin Bus staff are going undercover in an attempt to catch passengers who smoke illegally.
Illicit smoking of both cigarettes and cannabis on public transport is on the increase.
Dublin Bus said it had enlisted plainclothes staff to combat the problem and catch passengers in the act of lighting up.
"Unfortunately the situation has deteriorated over the past 12 to 18 months with people smoking on buses", a spokesman for Dublin Bus said.
However, prosecuting people who smoke on public transport is difficult because a witness is needed to confirm that an offender has lit up, something many passengers are reluctant to do.
