Bidders for General Motors Corp.'s (GM) German Adam Opel GmbH unit are expected to discuss details of their offers with labor representatives Tuesday in what appears to be one of the final rounds of talks before a midweek decision on German government support.

Officials of Austrian-Canadian auto supplier Magna International Inc. (MGA) and Ripplewood Holdings LLC are expected for talks at the unit's headquarters in Ruesselsheim, Opel labor representatives said Monday.

A spokeswoman for Opel supervisory board member and labor representative Armin Schild added that representatives of Italian automaker Fiat SpA (F.MI) might attend as well.

Magna appears to be frontrunner for Opel. According to previous statements, Magna has teamed-up with Russia's Sberbank (SBER.RS) for a planned investment of around EUR700 million. Under the plan, which is backed by Opel's labor representatives, Opel's troubled parent would retain a 35% stake in the company. Sberbank would take a 35% stake as well, with Magna holding 20% and Opel's employees 10%. Magna didn't return calls seeking comment. A spokesman for Opel declined to comment on the bids.

The German government confirmed at a press briefing Monday that it aims for a decision by the middle of the week. Government spokesman Ulrich Wilhelm said Chancellor Angela Merkel had a telephone conversation with Russian Prime Minister Vladimir Putin Saturday, met with Magna's management on Sunday and aims to meet Fiat Chief Executive Sergio Marchionne in the first half of this week.

The government's task force has also talked with RHJ but the firm's bid for Opel is less complex than those submitted by Magna and Fiat, Wilhelm said.

Talks over the three bids appeared to have made some progress in recent days. Several German politicians stated that Fiat and Magna have sweetened their offers, but didn't provide details. However, there are still a number of questions to be answered by GM as the final decision on Opel's future is to be made in the U.S.

"We need considerable clarification from the American government, such as on brand rights and intellectual property," the governor of the German state of North Rhine Westphalia, Juergen Ruettgers, told reporters.

Germany's federal government and the states of Hesse, North Rhine-Westphalia, Thuringia and Rhineland Palatinate, which are home to Opel plants, are considering bridge financing for Opel to keep it operating if GM files for insolvency before Opel can be sold.

The financing, which will be given only if the government and the states regard at least one of the bid as sustainable, aims to give Opel more time for negotiations with potential investors. The interim financing of around EUR1.5 billion would be from state-owned bank KfW and regional banks of the states with Opel plants.

GM is "very likely" to file for bankruptcy, a Canadian union chief said Friday, amid a flurry of activity ahead of a possible prepackaged move into court. A so-called 363 filing splitting the company into "good" and "bad" parts and controlled by the U.S. government could come after a crucial U.S. union vote Thursday, according to people close to the situation.

A GM bankruptcy is likely to be much more complex than that of Chrysler LLC, which filed April 30, because of its sheer scale, the size of its international operations and its impact on the supplier industry.

 
   -By Christoph Rauwald, Dow Jones Newswires; +49 69 29 725 512; christoph.rauwald@dowjones.com 
   (Roman Kessler, Andrea Thomas, Doug Cameron, Nico Schmidt and Flemming Hansen contributed to this article.)