General Motors has cut overtime shifts at six North American full-size pickup and SUV plants in as demand for the vehicles falls amid high fuel prices and a sustained slow-down in the housing market.

A credit crisis in the mortgage industry has slowed new house sales, in turn slowing sales of the high-margin full-size pickup trucks favoured by the building trade.

GM spokesman Tom Wickham told Dow Jones the overtime cut began last Monday while the production reduction will last for the rest of this year. GM's inventory of full-size trucks and SUVs has swollen as demand has slumped, the report added.

According to Dow Jones, citing Autodata, at the end of July, GM had 114 days' supply of its Chevrolet Silverado pickup truck, and 120 days' worth of the similar GMC Sierra.

But the news agency noted that those numbers are down 20% from June, thanks largely to the traditional July summer shutdown at GM plants. Inventory of those key vehicles is nonetheless up significantly from July 2006, and is much higher than the current vehicle stocks of most of GM's competitors, while GM's light-truck sales were off 9% for the first seven months of 2007, the report added.

"Overtime is used when there is a high demand for a product," Wickham told Dow Jones. The automaker is now slowing production as an attempt to avoid the prolonged practice of offering "excessive incentives" on the vehicles, the spokesman added. The news agency noted, hoever, that reducing overtime will cost GM revenue because vehicles are booked as revenue when they come off the assembly line.

"We had expected these cuts to come later this year," Baird analyst David Leiker was quoted as saying said in a research report. With the cuts occurring now, he said, "we believe this signals vehicle sales are weak, and are expected to remain weak."