Den Black, a retired General Motors Corp engineering executive, says he's worried and angry. The government-supported automaker is going bankrupt, he says, and he's sure some of his retirement pay will go down with it.

"This is going to wreck us," said Black, 62, speaking of GM retirees. "These pledges from our companies are now garbage."

As the biggest US automaker teeters near bankruptcy, workers and retirees like Black are bracing for what may be $16 billion in pension losses if the Pension Benefit Guaranty Corp (PBGC) has to take over the plans, according to the agency. As many as half of GM's 670,000 pension-plan participants might see their benefits trimmed if that happened, an actuary familiar with the company's retirement programs estimates.