A union representing workers at British confectioner Cadbury asked hostile bidder Kraft for a promise on employment security on Monday, saying it was increasingly worried about massive job losses.

Unite, Britain's biggest union, said on Monday it had written to Kraft chief executive Irene Rosenfeld about the 10 billion pound ($16.5 billion) cash-and-shares bid.

Unite asked for commitments there would be no compulsory redundancies and protection for employment terms and pensions.

Cadbury is a successful, profitable company that provides high quality jobs for over 6,000 employees in the UK and Ireland, and to date nothing has been said by Kraft to allay the concerns that we have about the potential threat to jobs and conditions should a takeover bid be successful, Unite quoted union official Jennie Formby as saying in the letter.

The union said Kraft's lack of detail on possible job cuts or site closures was unacceptable. Last week Unite said a meeting with Kraft had been constructive.

British trade unions do not wield the kind of power enjoyed by organized labor in some other European countries, but disquiet among Cadbury workers could add to pressure on Kraft, which already faces opposition from the company's management and from skeptical investors hoping for a higher offer.

The most important thing that came out of the meeting was an agreement to continue the dialogue, Kraft spokesman Michael Mitchell said.

Some of the guarantees that they sought, we are unable to make those guarantees until we can get into those facilities, and we are not able to do that.

Kraft is preparing to post formal offer documents to shareholders by December 7. Cadbury shares are trading significantly above Kraft's initial offer price -- at 1540 GMT they stood at 808-1/2 pence a share, nearly 13 percent more than Kraft's offer, which was worth about 717p at that time.

Most of the other big players in the global confectionery industry -- Hershey, Italy's Ferrero and Switzerland's Nestle AG -- are weighing potential bids, according to Reuters sources and media reports.

Many analysts doubt whether any of these three would bid alone, but possible combinations of them could trump Kraft's offer or push the American food giant to raise its offer.

(Reporting by Quentin Webb in London and Brad Dorfman in Chicago; Editing by Andrew Callus)