The GMB union said that the takeover approach of AstraZeneca by US drugs giant Pfizer has created added insecurity for workers and that any bid should be referred to competition authorities.
It called for a "bankable commitment that manufacturing and R&D [research and development] will continue here" amid fears these could be exported to the Far East.
GMB national officer Allan Black said the Government had a duty to protect against a "hostile approach" which would see business going abroad, adding that such a move would also weigh on the balance of payments deficit.
Lord Sainsbury, the billionaire of supermarket fame, said that under no circumstances should any takeover deal be allowed to go ahead.
US pharmaceutical giant Pfizer has made a second attempt to takeover AstraZeneca. Here are some of the main points of the possible deal.
How a tie-up between two of the world's biggest pharmaceutical firms would affect Britain.