There are worries about job implications if Vauxhall is sold
Italian carmaker Fiat has denied a report that it would cut 18,000 jobs and 10 assembly and component sites if it reached a deal with GM Europe.
Germany's Frankfurter Allgemeine Zeitung newspaper said that the cuts would include both Vauxhall plants in the UK and two Fiat factories in Italy.
It cited an internal Fiat strategy plan dated 3 April.
In response, Fiat said the information was not generated by Fiat and did not form part of any plan prepared by Fiat.
Fiat has begun efforts to win support for its plan to take over General Motors' European business, which includes Vauxhall and Opel.
Fiat chief executive Sergio Marchionne met German officials on Monday to discuss an offer for Opel.
The Frankfurter Allgemeine Zeitung report said that Vauxhall assembly lines in Luton and Ellesmere Port, as well as the Opel factory in Antwerp, Belgium, would be among those shut down, along with Fiat factories in Pomigliano, near Naples, and in Termini Imerese, Sicily.
Three Opel plants producing gearboxes - Bochum, Kaiserslautern and Ruesselsheim, Germany - would also be partially shut down, it added.
GM faces potential bankruptcy in the US and is under pressure to sell its European interests as it restructures.
Fiat also plans to take over some of Chrysler, the US carmaker that has applied for bankruptcy protection.