Trade union Unite has expressed concern about cutbacks if US firm Kraft Foods takes over Cadbury, the British confectionery group that employs several thousand people at factories in the West Midlands and Somerset.
"We need to know more about Kraft's plans and what they envisage for the UK workforce," said an official. "Mergers too often end in misery for employees, but we hope that this one doesn't. We are seeking reassurances."
Kraft last week proposed a £10bn takeover of Cadbury, which was rejected as too miserly. The City expects the Americans to come back with a sweetened offer, possibly as early as this week.
Union worries come amid fears for the future of Vauxhall's Luton plant after last week's deal for the takeover of GM Europe by Canadian group Magna, backed by Russian investors.
Irene Rosenfeld, Kraft's chief executive, has sought to allay fears by saying that the firm would invest at Cadbury's Bournville factory in Birmingham and at Somerdale, based in Taunton, Somerset. She said: "Our current plans contemplate that the UK would be a net beneficiary in terms of jobs."
Unions remember that Kraft took over Terry's, only to close the York factory in 2005, shifting production abroad.
Analysts say possible counter-bidders include Hershey's, Nestlé and Pepsico.