The rules have changed

Back in the day, if a natural resource company started screwing around, a government would just expropriate the company, or at least would threaten to do so..
So if BHP Billiton started screwing around with Saskatchewan potash mines -- like, shutting down mines because they were playing hardball on royalties or some other corporate game -- could the Saskatchewan government just expropriate the mines?
Not really, not anymore -- NAFTA would be angry. And we wouldn't like NAFTA when its angry...