The group, which calls itself the Unofficial Committee of Family & Dissident GM Bondholders, said large institutional bondholders weren't looking out for the little guys in their negotiations with GM and the U.S. Treasury last month.

"It is likely that because of hedging strategies and federal bailout funds, the larger institutional holders, who through their own committee participated in prefiling negotiations and 'accepted' the pending distribution plan, are to recover significantly more in relation to their holdings and are under vastly different pressures to accept the proposed transaction than the family and dissident holders," the group said in a new court filing.

GM Bondholders, who were owed a total of $27.2 billion by GM, are slated to receive 10% of a reconstituted GM after it emerges from bankruptcy, under GM's plan.

Bondholders also would get warrants to acquire 15% of the company if it reaches certain levels of success.

More than 54% of the bondholders agreed to the deal prior to GM filing for bankruptcy protection last week, according to the company.

The new group, which emerged in court records this week, said it is in communication with 1,500 bondholders through two bondholder groups and hopes to represent them and their holdings of more than $400 million in GM debt.

Legal papers filed by Patton Boggs LLP, described the group as consisting of family and noninstitutional bondholders "who have had no opportunity to participate in negotiations, no access or means to engage in hedging strategies, no access to federal bailout funds and no meaningful opportunity to have their important, distinct and different situation heard and represented in this case."

"For many of them ... the relevant question is not how much money can be made on the deal, but how much of their life savings will be lost," the filing said.

The bankruptcy court scheduled a hearing for June 23 on whether the small bondholder group should be made an official committee.

"The office of United States Trustee appointed a 15-person committee, ... and we do not think that it's warranted to appoint special committees," said Stephen Karotkin, a GM bankruptcy lawyer with Weil, Gotshal & Manges.