Both models apparently have a problem with oil leaking onto the exhaust manifold under hard braking. If the oil makes it underneath the manifold's heat shield, it's possible that it could ignite a small flame which could spread to the spark plug covers. The engine fire normally happens five- to ten-minutes after the vehicle has been shut down, and GM is suggesting that all of the 207,542 vehicles affected shouldn't park inside garages, carports or other parking structures until the required fix is completed. The recall notices were sent out today, so we'd suspect that dealers should have the necessary parts in stock by the end of the month.
Until NHTSA's site gets back online, follow the source link below for the full directive.