The only person representing individual General Motors Corp. (GM) bondholders on a committee negotiating a debt exchange with the auto maker resigned from the group on Tuesday.

Jim Graves, a former software developer from Celebration, Fla., who is part of a group called the Main Street Bondholders, said he couldn't bring himself to either support or reject GM's proposal that bondholders swap $27 billion in debt for a 10% stake in GM.

It's the latest sign of resistance to GM's efforts to slash debt ahead of an increasingly likely bankruptcy filing.

"I did not want my continued participation on the committee to in any way compromise our ability to act in our best interests going forward," Graves said in a statement.

GM and the U.S. Treasury had been in negotiations with the bondholders committee, which until recently was comprised of institutional bondholders. A separate group of individual bondholders who hold about 20% of GM's bond debt recently began to organize in protest of the offer. As part of that effort, Graves joined the ad hoc committee. He wouldn't comment on why he resigned beyond the statement.

GM has said it will be forced to seek bankruptcy protection by June 1 if it doesn't get 90% of bondholders to agree to the offer, which could leave them with pennies on the dollar from what they are owed by GM. The auto maker has conceded a bankruptcy is the "probable" scenario.

The offer expires at midnight. GM is expected to disclose Wednesday how many bondholders signed off on the debt swap. As of Tuesday evening, the number was very low, according to people familiar with the exchange.

The auto maker could decide to extend the deadline for the exchange to appeal to more bondholders, a decision the company said it would make on Wednesday.

Graves previously had said he and his mother stand to lose most of $100,000 in GM debt they were counting on for retirement.

-By Sharon Terlep, Dow Jones Newswires; 248-204-5532; sharon.terlep@dowjones.com