Union officials representing thousands of UK workers employed by Heinz are seeking urgent talks with a consortium buying the food giant to seek assurances about UK jobs.
Heinz says it had agreed to be acquired by an investment consortium including billionaire investor Warren Buffett in a deal valued at 28 billion dollars (£18 billion).
The United States company says Heinz shareholders will receive 72.50 dollars (£47) in cash for each share of common stock they own.
Berkshire Hathaway and 3G Capital, the investment firm which also bought Burger King in 2010, say Heinz will keep its headquarters in Pittsburgh.
Unite national officer Jennie Formby said: "Whilst we recognise the commitment given by Berkshire Hathaway that it will be business as usual following the surprise change of ownership announced today, the 3,000 Unite members who work for Heinz in the UK will want more detailed assurances that their jobs and sites will remain secure.
"Unite will be seeking an early meeting with senior management to allow us to explore in greater detail what impact, if any, this acquisition will have for the UK business."