The Justice for the Forgotten organisation has held a wreath laying ceremony in Dublin to mark the 40th anniversary of the Sackville Place bombings.
Two CIÉ workers, Thomas Duffy and George Bradshaw, were killed and scores of other people were injured when a car bomb exploded on 1 December 1972.
Lord Mayor of Dublin Naoise Ó Muirí and Dublin Bus CEO Paddy Doherty attended today's ceremony.
The oration was given by SIPTU General Secretary Jack O'Connor.
The Sackville Place explosions coincided with a crucial Dáil debate on an amendment to the Offences Against the State Act, which aimed to strengthen the State's power to deal with the IRA.
Following the blasts, Fine Gael withdrew its opposition to the bill and it passed.
A third CIÉ worker died in a similar incident the following month.