Pointing out Kraft's huge debt of £22 billion, the country's biggest trade union said that at least 7,000 jobs may directly be at risk as Kraft ownership could see control of Cadbury move from the UK to Illinois in the US.
The US food giant would want to slash the number of British employees and cut borrowings after the takeover.
Unite added that an additional 20,000 jobs would be threatened in the wider supply chain that exists in the UK to serve Cadbury.
The dire warning by the trade union came close on the heels of media reports saying that the Italian company Ferrero has lost interest in the Cadbury bid race, thus strengthening the takeover chances of Kraft.
Unite in a statement said that between 2004 and 2008, Kraft shed 19,000 jobs and closed 35 sites to help pay down its debt.
Unite said that Cadbury specializes in making chocolates. Its brand value will get diluted if it gets absorbed in the crowded portfolio of Kraft's over 60 brands ranging from processed cheese to groceries.