The ad-hoc group holding just under half of General Motors Corp.'s (GM) subordinated debt said they haven't been contacted with news of any new offer, according to a person close to the bondholders.

The offer, reported earlier in the day on CNBC, of up to 20% of equity in the firm was seen by traders as a low-ball estimate coming from GM or the government. The person close to the bondholders said bondholders have yet to see an offer and have not participated in negotiations.

Calls to the Obama Administration and GM were not immediately returned for comment.

News of the reported offer comes as the clock continues to tick down to the administration's June 1 deadline for a viable restructuring plan from the ailing auto giant. The government has hired its own team of consultants and lawyers who are consulting with GM insiders to beat the deadline. With the government and company both raising the specter of a potentially disruptive bankruptcy filing, tensions are high.

"It's all brinksmanship at this point," said Jon Duensing, head of credit trading at Smith Breeden. "At this point I don't think the bondholder group has a lot to lose anyway, so I would imagine they are pretty resolute in their position."

Duensing said he is not involved with the ad-hoc group, but has been working with his team on strategies for GM bonds. He said they are actively contemplating the possibility of the government changing the bondholders' contracts and "cramming them down" to limit their rights.

"This is very far fetched, but we're in a far-fetched type of situation right now," Duensing said.

The person close to the bondholders was skeptical of the reported offer. With some $27 billion in unsecured claims outstanding there would have been a total of $135 billion or more in other claims on GM's equity for them to end up with just a fifth of the company - assuming a standardized bankruptcy proceeding.

-By Andrew Edwards, Dow Jones Newswires; 201-938-5973; andrew.edwards@dowjones.com