Fiat plans to cut almost 10,000 jobs if it succeeds in buying Opel and Vauxhall from General Motors.
The Italian automaker said the cuts would be made across Opel's operations in Europe, which currently employ about 50,000.
A rival bidder, car parts maker Magna, has pledged to keep Opel's four German plants, but made no comments about the two Vauxhall factories in Britain.
The third bidder is RHJ International, a Brussels-based investment firm.
The BBC reports German government officials are discussing the bids, which were submitted before Wednesday's deadline.
Unconfirmed reports suggest a fourth bid may have subsequently been tabled by a Chinese company, Beijing Auto.
General Motors aims to sell Opel ahead of a deadline of 1 June set by the US government to restructure its finances and avoid the need to go into bankruptcy protection.
GM is also looking to sell Sweden-based Saab, its other European car business.