The officials did not know if the ban affected just their plants or if it was companywide.

GM spokesman Tony Sapienza said Monday that the company has not announced any ban on unscheduled overtime, but it is looking at ways to conserve cash.

'Officially we haven't told employees anything,' he said. 'As we weather very difficult economic conditions, we're looking at a variety of ways to be as efficient as possible while balancing the needs of the market for our products.'

Unscheduled overtime generally is used when a worker calls in sick. An employee who is on duty at the time usually works half the shift for the sick employee, and another worker is called in early to work the other half.

The union officials were unsure how the company would fill assembly line positions for those who are ill.

Jim Graham, president of UAW Local 1112 in Lordstown, said GM probably will have to make an exception at his plant because its small cars are selling.

'We will have to. We need the cars,' he said.

Through September, Cobalt sales were up 6.3 percent and G5 sales rose 1.7 percent, even though overall U.S. light vehicle sales were down 13 percent compared with the first nine months of 2007. Malibu sales are up 51 percent, while G6 sales have risen 8.4 percent, according to Autodata Corp.

GM's sales through September are down 18 percent, and industry analysts are predicting that October could be worse than September, which had the lowest overall U.S. sales level in more than 15 years. Dealers have reported that higher credit standards on the part of many lenders, as well as economic uncertainty, have kept many buyers away from showrooms in October.

Several analysts predict that Detroit-based GM will burn up so much cash that it will reach its minimum operating cash level of $14 billion sometime next year. The company has lost $57.5 billion in the past 18 months, although much of that comes from noncash tax accounting changes.

Last week, GM said it would eliminate around 2,700 jobs by shuttering a metal stamping factory in the Grand Rapids suburb of Wyoming by the end of next year and speeding up the closure of its Janesville, Wis., sport utility vehicle plant, with most of that facility closing Dec. 23.

The company also announced that it would cut production at plants in Detroit, Pontiac and Wilmington, Del., putting another 1,600 workers on indefinite layoff.

Analysts say with the slow sales, it's likely GM will announce further production cuts and possibly more plant closures.

GM and Chrysler LLC's owner, Cerberus Capital Management LP, are discussing the possibility of GM acquiring Chrysler. GM's motivation, according to a person with knowledge of the talks, is that Chrysler has about $11 billion in cash that GM could use to stay afloat if the credit markets remain tight.

GM and Chrysler have said automakers talk all the time, but they won't comment specifically on the talks.