Sixty jobs are to go after it was announced that the Anglesey Aluminium factory will close.
Local politicians warned of a jobs crisis on the island with confirmation that the Penhros plant will stop operations within two months, with 20 workers kept on until the site is sold.
The Holyhead smelting operation shut in 2009 with the loss of nearly 400 jobs.
The remaining 80 staff have been at the plant as part of a decommissioning process and its re-melt business.
The company said it had made "extensive effort" over the past few months to identify ways to make and save money to offset the "substantial losses" facing the business.
It said it had been struggling because of more competition, material cost increases and a drop in demand for its products.
Anglesey Aluminium - which started production in 1971 and was once one of the largest employers on Anglesey - started consulting with the workforce in December.
Klaus Stingl, chairman of the Anglesey Aluminium Metal (AAM) board, said the priority now was to ensure workers were helped to find new jobs.
"The health and safety of AAM's employees will remain of paramount importance in this difficult time with additional workplace support being given to employees to help them seek alternative employment," he said.
"This will be similar to the efforts made by AAM in 2009 when 400 people were made redundant due to the company not being able to gain a commercially viable power contract."
'Extremely disappointed'
Before the decision to close the factory, it was hoped it would remain open until June 2014.
Plans have been announced for a biomass power station, a fish farm and a holiday park on the site.
Mr Stingl said AAM will work with the UK and Welsh governments and Anglesey council to make sure these go ahead "in an effort to create a legacy for the local community by the creation of alternative employment opportunities".
Anglesey AM Ieuan Wyn Jones said he was "extremely disappointed" by the news of the closure.
"The loss of jobs on the island in the current economic climate is a big blow to the local community and we must be redoubling our efforts to conclude negotiations for new investment to the site as soon as possible," he added.
Local MP Albert Owen said it was clear that Anglesey had a "jobs crisis" following this news, as well as Vion's recent confirmation that 350 jobs are under threat at its Welsh Country Foods plant at Gaerwen.
"I will work with all stakeholders, government, businesses and the unions to limit the impact of any job losses, but we need a bold jobs plan for the near future," he said.
Anglesey Aluminium is jointly owned by Rio Tinto Alcan and Kaiser Aluminium.