A strike by the United Auto Workers union has caused a parts shortage, forcing General Motors to shut down its pickup truck and transmission factories in Silao, Mexico.

Spokesman Dan Flores confirmed that production at the factories ended Tuesday morning, affecting 6,000 workers.

The plant shutdown means GM has lost any new supplies of its light-duty Chevrolet Silverado, the company's top-selling U.S. vehicle. Earlier GM had to close a Mexican engine plant and an assembly plant in Canada due to the strike.

The strike by over 49,000 union workers is now in its third week, and both sides are feeling the impact. More than 4,000 workers at GM's Arlington assembly plant, where the automaker produces large SUVs, are among the strikers.

Workers are having to get by on $250 per week in strike pay instead of their normal base pay of about $1,200 per week.

The losses are mounting each week the strike continues, costing GM about $480 million in the first week and another $575 million in the second, Brinkman wrote. The company is losing $82 million a day.

GM books revenue from building vehicles as soon as they change hands from the factory to the company that ships them to dealers. So revenue has been counted already for nearly all vehicles that are in dealer hands. Many dealers stocked up before the strike and report having plenty of inventory.

Brinkman wrote that GM could recover some of its lost profits by increasing production in the fourth quarter once the strike comes to an end. But the company likely will be limited to add production of vehicles that already are in high demand or where new models are being launched, such as GM's heavy-duty Chevy Silverado or GMC Sierra pickup trucks, Brinkman wrote.

GM's pickup truck and large SUV plants already were working six or seven days per week to meet demand before the strike, so increasing production will be difficult.