Workers at the Dow Corning factory in Barry have been told about the potential impact on the site because of a restructuring of the company.
About 630 people work at the plant, and a 45-day consultation will begin soon.
The company stressed, however, that the decision has "absolutely nothing to do with Brexit".
Dow Chemical Company has announced it will cut about 2,500 jobs worldwide, or about 4% of its total workforce.
In a statement, the firm said: "The leadership met with employees at the site to talk about the rationale for this global workforce consolidation and the possible impacts to the roles at Barry."
Silicone production began at the Barry site in 1952, initially by a company called Midland Silicones.
Dow Corning's website describes it "as one of the most advanced facilities in the world" of its type.
It says: "Silicone fluids, rubber and specialty polymers made in Barry are used in a wide variety of applications, from cosmetics to car airbag coatings and construction sealants."
About 115 jobs are under threat at a chemical plant in the Vale of Glamorgan.