The board of the Rail Procurement Agency, which oversees the Sandyford and Tallaght tram lines, will decide shortly on allowing carriages to be used for advertising.

"No decision has been made yet but it is something we are considering, " an RPA spokesman said. "A key consideration will be whether or not this would fit with the image of the city, " he added.

The lucrative advertising would generate several million euro a year. However, Aidan Culhane, Labour Party candidate for Dublin South, has called on the RPA to reject the idea, which would see the standard grey carriages replaced by commercial advertising.

"The Luas has come to be identified with Dublin. It would be a real pity if the Luas was turned into an advertising hoarding. The entire elegant look of the carriages would be thrown away, " Culhane said.

Culhane is the first general election candidate to use the Luas for political advertising, with his posters placed on the inside advertising spaces in carriages on the Sandyford to St Stephen's Green line.

The two Luas lines currently carry about 70,000 passengers a day. The RPA has said any profit from advertising revenues would be reinvested in improvements in the service.