The Menai Suspension Bridge will be closed this weekend as the second phase of maintenance work continues.
The Welsh Government says unsecured communications cables beneath the structure pose "an immediate safety risk".
Scaffolding has already been installed, but the cables, which provide links between Anglesey and Ireland, must be secured before work can continue.
One lane has been closed since Wednesday between 10am and 6pm, but the bridge will be closed entirely to traffic from 2pm on Friday (15th May) to 6pm on Saturday (16th May).
Next week, the one lane closure will resume each day between 10am and 6pm until Friday, a day before the Urdd National Eisteddfod at Mona.
Diversions will be in place via the Britannia Bridge and pedestrians and dismounted cyclists will be able to cross the bridge.
Last month, the bridge was closed twice for safety inspections after it was crosssed by overweight vehicles.
A Welsh Government spokesperson said: "Every effort will be made to minimize disruption while this important work is carried out, and we thank the community for their continued patience."
"Enforcement of the 7.5 tonne weight limit remains essential for maintaining safe operation of the bridge while works are underway. If a vehicle above this limit crosses the bridge it then has to be closed for a full inspection."
"Adherence to the speed limit on the bridge is also essential for the safety of the workforce."
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