Textiles firm DuPont SA has said it could close its Pontypool plant with the loss of up to 60 staff.
The company issued a statement on Wednesday afternoon blaming "extremely difficult" trading conditions for the situation.
DuPont manufactures polyester filaments yarns for the car and clothing industry and the company has decided the Mamhilad plant is "no longer viable".
The Transport and General Workers' Union has said talks with management would look to minimise the impact of closing the plant.
Today's announcement is the final act in their strategy to move production to their Turkish facilities."
John Burgham, T&G branch secretary DuPont SA
T&G branch secretary John Burgham said if the plant closed, it would be a "disaster" for Pontypool town.
DuPont's statement read: "It's the opinion of the company's leadership team that continued production of Polyester filament products at the Pontypool site is therefore not viable in the future, and that the remaining assets at Pontypool will probably have to close."
Thirty contract workers are also set to lose their jobs at the plant.
The company has said that support would be offered to workers in the event of job losses.
The T&G believes the problems lie with DuPont's decision to switch production to Turkey and the union has called on the UK Government to do more to protect British manufacturing jobs.
During its peak, the former ICI and British Nylon Spinners plant employed 8,000 workers.
John Burgham added: "The workforce at the plant have moved mountains to try and prevent this decision, their productivity and skill levels are second to none.
"We believe that Dupont SA has had a game plan to close Pontypool for some time now.
"Today's announcement is the final act in their strategy to move production to their Turkish facilities."
'Support the workers'
T&G regional secretary Jim Hancock said the union had been warning about the erosion of manufacturing jobs in Wales.
"Dupont SA's actions are a stark demonstration that our fears are a continuing reality.
"We are calling upon the Welsh Assembly Government to do all that it can to support the workers at Dupont SA through this difficult time.
"The exodus of well-paid jobs to low paid areas of Europe is decimating Welsh manufacturing.
"It is important for the Welsh Assembly Government to make the case to Westminster that the sooner they implement the Information and Consultation Directive the better."