A new report has found a section of Dún Laoghaire's East Pier is at risk of structural failure.
The unpublished engineers report commissioned by Dún Laoghaire Harbour Company and obtained by RTÉ's Morning Ireland, warns that repairs to a 75-metre section of the pier will cost more than €1m.
The pier, which was built almost 200 years ago, is visited by more than one million people annually.
The Harbour Company said the pier will not need to close while repair work is undertaken.
The report, compiled in February, details how structural beams, which support an area of the pier known as Berth 1, are at risk of corrosion and failure.
The berth, which is located alongside the pier, was added after the original construction to facilitate boats mooring alongside the pier itself.
It is also the location for Dún Laoghaire's proposed urban beach, which was granted planning permission last week.
The Harbour Company has said repair work will dovetail with the construction of the new amenity, which is scheduled to open in 2016.
Dún Laoghaire Harbour Master Simon Coate said: "Steel reinforcing has reacted over the years.
"It has been open to the sea for a long time.
"That needs repairing and there is a process to do that by breaking the old concrete and reinforcing it."
"The platform is completely safe but it can't take really heavy loads and that's why we have put bollards along to stop heavy loads going on," he added.
The cost of the repairs is estimated by the engineers report to be between €1m and €5m.
Local Fine Gael Councillor Barry Ward is calling for the work to be undertaken as a matter of urgency.
"It is not dangerous to people now, but how long will it take before it becomes dangerous? The worst-case scenario is that there is structural failure and a part of it breaks."
Cllr Ward added that it would be "deeply irresponsible" if delays in the repair work led to the commercial and leisure capabilities of the pier being limited.