Chemical firm Dow is set to cut nearly 300 jobs at its Barry works.
The chemical manufcaturing firm - one of the Vale's biggest employers - has confirmed it plans to close down the basics area at its Cardiff Road site within the next three or four years.
It's understood 291 workers are affected - around a third of the workforce at the Barry plant, which is expected to focus on making downstream silicones.
A consultation with employees is now underway with no redundancies expected until the middle of next year.
According to union officials, it's believed the corporation is blaming "cheap competiton" from China.
In a statement on Monday afternoon, a Dow spokesperson said: "As part of Dow’s assessment of its European assets, the company has identified the basics siloxanes operations at Barry, U.K. among other upstream portions of Dow’s portfolio that will require further action."
"The potential outcome identified at this time for Dow’s basics siloxanes operations at Barry is a shutdown."
The statement added: "Siloxanes production is one of several manufacturing facilities and operations at our Barry site, which in total employs approximately 850 employees and contractors."
"This potential shutdown would help strengthen the Company's competitive position in the specialty silicones market in Europe and the U.K."
"The production of specialty silicones in Barry will continue, supporting key markets such as automotive, electronics, energy, construction, and personal care."

The Unite union says its calling on the US-owned to reconsider its decision and work with them to avoid compulsory redundancies.
Unite secretary general Sharon Graham said: "It is outrageous that valued workers are being punished for a situation not of their control."
"The potential loss of so many well paid jobs in the area will be devastating, not just to our members and their families, but to the local economy as well."
The Barry works were opened in 1941, initially under the ownership of the Ocean Salts company. Dow Inc. arrived in 1971 when it took over the site from Midland Siicones and now employs around 850 people working around the clock.
Dow makes use of basic chemicals internally as raw materials, which are also sold worldwide in areas such as the food industry, paints and coatings and dry cleaning products.
In 2021, the corporation was ranked as among the three largest manufacturers of chemicals in the world - with 214 sites across 37 countries.
But according to the Unite union, Dow says its basics product are no longer competitive on the open market with China undercutting prices.
Unite regional officer Richard Jackson said: "Unite is calling on Dow to reconsider its decision and work with us, government and other stake holders to find an alternative solution to this closure."
"Unite is also calling on Dow to work with the union in order to avoid compulsory redundancies and to seek to protect as many jobs as possible. The union will ensure it is involved all the way throughout this process."

Three CoastSnap stations set to be installed along the Glamorgan Heritage Coast
Daffodil Runner statue installed at Marie Curie Hospice in Penarth
Woman Dies After Incident in Leckwith as Police Investigation Continues
Vale entrepreneur wins national Innovate UK award for sustainable construction technology
Cardiff Airport retains top accessibility rating as regulator reports record demand for assistance
Open Doors event to showcase hidden world of Glamorgan Archives
New details have emerged of a new tree-lined public square that will replace a traffic dominated junction
Dyffryn Gardens’ Edwardian rose garden blooms again after decade-long restoration
Barry’s Own Daniel White to Walk 190 Miles Back to Where His Round Table Story Began
1,300 people attend Flying Start Family Fun Day
Dispersal order put in place to tackle anti-social behaviour
Interim Chief Executive Appointed at Cardiff and Vale University Health Board
Cardiff Theatre Marks 50 Years of Service for Long‑Standing Staff Member
Council to review use of GP letters as evidence for disability claims
Plans have been put in place to redevelop a complex with more than 20 flats
Vale Council Reaccredited Under White Ribbon Scheme as Part of Ongoing Work to Tackle Violence Against Women and Girls
Two Vale Restaurants Among Those Set to Close as Whitbread Shuts Brewers Fayre and Beefeater Chains
Vale Council Issues Safety Warning After Gas Canisters Found in Household Recycling
Cogan Primary School Praised for its Inclusive Culture and Strong Leadership in Estyn Inspection