A CD and DVD factory near Cwmbran in south Wales is to close with the loss of 310 jobs.
Thomson Technicolor blamed competition, price pressure and a slowdown in demand for the decision to shut its plant at Llantarnam.
Torfaen AM Lynne Neagle said there had been uncertainty for some time but it was "terrible news" for Cwmbran and the plant's workforce.
The California-based company has not yet announced the date of closure.
A spokesman for Welsh Enterprise Minister Andrew Davies said he was "disappointed by this announcement" and was looking for a meeting with the company to discuss the decision.
He said: "Together with our partners from across the public sector, we will be working to identify what support can be provided to help those affected."
'Difficult period'
Ms Neagle added: "I have been in touch with the Amicus representative for Technicolor over recent months, as there has been uncertainty about the future of this plant for some time.
"I will be meeting again with union colleagues as soon as possible."
A Thomson Technicolor spokeswoman said that the exact date of closure was subject to a consultation process, which has now begun.
In a statement, the company said the proposed changes were being announced to give workers time "to properly prepare for the future and to ensure an orderly transition of operations to the remaining designated facilities".
The statement added: "The company will work to assist these employees during this difficult period of time."
On its website, the California-based company claims to be "the world's largest independent optical disc and video manufacturer".
It says the company, which has offices worldwide and also makes movies, has the ability to make 1.5 billion DVDs a year.
Customers include Paramount, Twentieth Century Fox and The Walt Disney Company.
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