Anglesey Aluminium has announced an additional 250 job losses at the north Wales smelting plant. This is in addition to 140 jobs losses that were previously announced.
The company is the biggest user of electricity in Wales and has a long term energy partnership with Wylfa nuclear power station. This agreement is due to end in September.
The UK government has offered the plant £48m to help keep production on the island but the company has rejected the offer saying that it would not cover the firm's energy costs after its current partnership with Wylfa ends.
Managing director David Bloor said the plant needs a long term plan from the government to deal with Anglesey Aluminium's energy needs.