The exact date of shut down is not yet known, but reports suggest that it will happen around the normal two-week shutdown in July when changes are made from one model year to the next. However the employees are not yet informed about the closure.
The shutdown may result in huge job loss. However the workers laid off would still get most of their pay because their United Auto Workers union contract requires the company to make up much of the difference between state unemployment benefits and their wages. But the shutdown could be even more catastrophic to many auto parts suppliers that are near bankruptcy due to previous production cuts. During the shutdown, suppliers could not ship parts to GM and would lose critical revenue.