Another 1,500 workers at three General Motors Corp. plants will be laid off indefinitely over the next few months due to decreasing demand for many products, the International Herald Tribune reported on its website.

GM, which posted a $15.5 billion net loss in the second quarter, has been battling an industry sales slouch in the United States. Its 2008 U.S. sales were down nearly 18 percent through September.

GM plans to lay off 700 workers at its Pontiac Assembly plant, about 400 hourly workers each at its Wilmington, Del., assembly plant and its Hamtramck Assembly plant, GM spokesman Tony Sapienza told the newspaper.

“The market continues to struggle across the industry,” Sapienza said. “We continue to adjust to the demand … as the economy picks up you will probably see us adjust production upward as well.”

Industry analysts say the slumping U.S. auto market will force GM to shut down more plants. U.S. sales overall are down 13 percent for the first nine months of this year, with calculations that automakers will sell 2 million fewer vehicles than they did last year.