Mars, the maker of chocolate bars and sweet drinks, has launched a review of its European business in an effort to boost sales and become more efficient.
Mars said changing market conditions have prompted its review
The review will focus on "sales growth, manufacturing capacity and overheads, and ways of working", the company said.
Rumours have been circulating for weeks that Mars wants to close its operation at Slough, near London.
Mars said on Sunday that the review will take six to eight weeks and it was too early to discuss possible outcomes.
"I will not comment when nobody knows what the outcome of the consultation will be," said Michael Jenkins, director of external affairs at Mars' Masterfoods division.
A need to talk
Mr Jenkins told BBC News that the review was part of ongoing attempts by Mars to improve its business and the firm would talk to its 11,000 European staff before making any decisions.
"We are no different to many other fast-moving consumer good companies," Mr Jenkins said, adding that Mars faced "challenging conditions" and the need to adapt to "changing competitive landscapes".
Mars is one of the world's biggest confectionary companies, with brands including Mars, Snickers, Twix and M&Ms. It also produces pet products and food including Pedigree and Uncle Ben's rice.
The company employs about 1,600 people at its Slough office and has another six sites in the UK
Union and local government officials said staff at Slough are concerned about their future, according to a report in the Sunday Times newspaper.
Frank Loveday, of the Bakers Food and Allied Workers Union, was reported as saying "staff feared the company was set to make big cuts". Rob Anderson of Slough Borough Council said "rumours that Mars is pulling out make for worrying times".