More than 400 jobs were announced at the Kent plant in 2007
Up to 240 jobs are under threat at the pharmaceutical firm Pfizer's research and development site in Sandwich, Kent.
The company said it was part of a move to improve efficiency which would see between five to eight per cent of the global workforce facing redundancy.
Pfizer said up to 800 scientists would be laid off in its latest effort to refocus disappointing research efforts.
It has begun a 90-day consultation period, but in a statement said it did not "make these decisions lightly".
"It's important to point out that this is an ongoing evolution of Pfizer Global Research and Development and Pfizer as a whole," the company said.
"We continually look for ways to operate our business more effectively and efficiently to create value for all of our constituents."
But the Labour MP for South Thanet, Steve Ladyman, described the news as disappointing.
"We can ill afford to lose any quality jobs and I am saddened that a site that has made such a huge contribution to Pfizer's fortunes is again going to see job cuts," he said.
"One job lost is one too many and each and every lost job will be a tragedy for the person and family affected."
Mr Ladyman added the "only positive thing" to come out of the announcement was that "all the areas of research carried out at Sandwich had been identified as going forward and the site has been identified as an important player in Pfizer's overall strategy."
He said he hoped the job losses would be as a result of voluntary redundancy or natural wastage.
In September 2007, Pfizer, which has its UK business headquarters in Surrey, announced the loss of more than 400 jobs in Sandwich with the closure of its manufacturing arm.