Around 340 employees have been told Aptuit's Riccarton and Livingston facilities will be closed over the next 12 months.
Sources say staff across the corporation were told of the closure of the 200,000 sq ft Riccarton plant, based within the Heriot Watt Research Park, and where the majority of workers are based, this week.
Aptuit, a drug development corporation, told the Evening News it had been affected by the "worldwide economic downturn". It said that some roles could be transferred to other facilties, but admitted the move could have a "serious impact" on employees and the local community.
One former senior employee in the company described the closures as a "another body blow to the pharmaceutical industry in Scotland."
A spokeswoman for US-based Aptuit said: "As a result of the continued worldwide economic downturn and pharmaceutical market dynamics, Aptuit is proposing a phased withdrawal from our facilities in Livingston and Riccarton, Scotland, over the next 12 month period.
"We will shortly enter into a 90-day consultation period with employees from these sites.
"Aptuit understands the serious impact that this may have, and if the proposals are implemented, would have on our employees and the community."
They added: "We will do everything possible to listen to our employees' needs and concerns and we are committed to exploring all available alternatives.
"In the event that a decision is taken to shutdown, we will provide significant transition support to our employees."
She added: "Aptuit remains committed to our other Scottish operations in Bathgate and Glasgow."
The work carried out at Livingston and Riccarton is primarily early development and preclinical work, such as toxicology studies, and provides high-level jobs for hundreds scientists and technicians.
Aptuit was founded in 2004 by Frank Wright and chief executive Michael Griffith, who acquired a set of research centres from Quintiles, the US drug-testing group, in 2005. It announced it was building a 20m laboratory complex housing 200 highly qualified scientists in Bathgate in 2006.
The Bathgate pharmaceutical research centre carries out clinical operations and consulting, including analyses and develop drugs for diseases such as diabetes and cancer for biotechnology companies, while the Glasgow site carries out pharmaceutical development & manufacture.
Ricky Henderson, whose Pentland Hills council ward includes Riccarton, said the announcement could not have come at a worse time for local families.
He said: "It's a dreadful time to get this kind of news certainly. High quality jobs are hard to come by and the reputation of the Heriot Watt campus is such that they have a good record of success. For that to be reversed is extremely worrying.
"I feel for the people and families who will be affected.
"I know that a lot of people who live in and around the Currie area work at the Heriot Watt campus in various capacities, so I can't help but think I'm going to have a number of constituents who will be impacted."
The Labour councillor added that he now plans to table an emergency motion at next week's full council motion to determine if the local authority can help the situation.
He said: "We'll see if the council can start looking at the situation and see if there's anything we can do to help.
"There are support networks for working with people when factories and firms close to find other opportunities, and I'll be urging them to do that."