General Motors Corp. (GM) is "very likely" to file for bankruptcy, a Canadian union chief said Friday, amid a flurry of activity ahead of a possible pre-packaged 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 on Thursday, according to people close to the situation.

A GM bankruptcy is expected 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 larger impact on the supplier industry.

While unions in the U.S. and Canada have tentative deals with the company, bondholders continue to hold out for better terms while the German government said the proposed sale of a majority stake in its European business needs to be resolved next week.

A group of U.S. lawmakers is also calling for fresh talks with GM bondholders, whose resistance to the proposed terms is viewed as the main barrier to a quick exit by the company from bankruptcy.

Ken Lewenza, president of the Canadian Auto Workers union, said in a media briefing Friday that GM is "very likely" to file for protection.

The CAW's pact follows the tentative deal GM reached with its U.S. union this week to convert health-care obligations into equity in a reorganized company, alongside wage and benefit concessions.

GM has said it is unlikely to secure final agreement from U.S. employees before the May 26 expiration of an exchange offer to bondholders that is widely expected to be rejected, pushing the company closer to a filing.

Europe In Focus

German politicians also signaled Friday that the company and the U.S. auto task force need to make a decision next week on three bids for the company's European operations.

GM has worked to ring-fence its international operations ahead of a U.S. filing, which is widely expected to follow the example of Chrysler LLC and take place in New York's southern district.

The auto task force requires that all of GM's regional operations be viable in order for it to approve a new restructuring plan and grant as much as $30 billion in fresh loans to keep it operating.

GM has received three bids for a majority stake in its European business, tied to German government funding, including one from prospective Chrysler LLC partner Fiat SpA. (FI-MI).

Fiat's cash-free offer would combine GM's Opel and Vauxhall brands with its own and Chrysler, cutting around 10,000 GM jobs.

The Italian company has signaled it may revive interest shown in GM's Latin American business at a later date.

Canadian parts maker Magna International Inc. (MGA) is seen as a frontrunner because it would offer some cash and provide more job guarantees, though neither GM nor German authorities have expressed a preference.

The company would reportedly pay EUR700 million for a 35% stake, in partnership with Russia's Sberbank (SBER.RS), and OAO GAZ Group (GAZA.RS).

The private-equity bid from RHJ International (RHJI.BT) may provide Opel with some cash upfront.

German Economy Minister Karl-Theodor zu Guttenberg said Friday that all options are still open for GM's Opel brand, including possible insolvency.

"We must have made a principle decision next week because in the U.S. they will make a decision regarding starting insolvency procedures [for GM Corp.]," he told Dow Jones Newswires.

Shares in GM, which are expected to effectively lose all value in a filing, briefly moved above $2 for the first time in a month having gained almost a third Thursday following the U.S. union deal. The stock later slumped and was recently trading down 16.1% at $1.60.

-By Doug Cameron, 312-750-4135; doug.cameron@dowjones.com

(Jennifer Clark, Christoph Rauwald, Sharon Terlep and Andrea Thomas contributed to this article.)