General Motors Corp. confirms it will lay off an undetermined number of hourly employees at its Pontiac (MI) Assembly Center, which builds heavy-duty versions of the recently redesigned Chevrolet Silverado and GMC Sierra pickups.

A company spokesman says GM notified workers at the plant on Monday afternoon, although it won’t estimate how many face layoffs. The Detroit News said earlier as many 500 workers would be idled. GM says a firm number could be reached by the middle of the week.

The auto maker is blaming the cuts on weakened demand for its heavy-duty pickups.