Residents in Dublin's North Strand and East Wall have begun a permanent blockade of Iarnród Éireann's East Wall Road replacement railway bridge.
The blockade began as Iarnród Éireann announced details of arrangements for the third weekend of work for the replacement bridge.
The residents claim Iarnród reneged on a decision to sign a legally binding agreement, which the company has denied.
Ms Fiona Moloney, of the North Strand Community Action Group, said Irish Rail had forced residents to maintain a 24-hour vigil to prevent machinery accessing the site.
The €20 million project entails building a replacement bridge, an additional railway track and a 100-metre concrete wall behind an existing wall. Ms Moloney said the development would put many residential properties into darkness.
Yesterday an Iarnród spokesman, Mr Barry Kenny, said they had not reneged on any agreement.
In April they had offered in writing to modify the project by removing the wall six months after the bridge's completion.
There was a draft agreement, and they were in the process of completing the full agreement.