I had to let someone go at a company we had just acquired in Montreal a few years ago. The guy was underperforming and had a huge attitude problem (bursts of anger actually). One of the frequent arguments he had with everyone was that he insisted he didn't need to learn French to live in Montreal and was somehow hostile to the language. I honestly questioned why he immigrated there in the first place.
Since this was an acquisition, it made it easy for us to do so. All we had to do was not to include him in the positions that would join the new company. Simple paperwork. He seemed to really want to come to the US but the performance and behavioral issues made it a big no. I don't think he would have passed the stricter requirements anyways.
Some companies like Google will even have engineers at certain acquired companies re-interview to transfer. The North acquisition was a poster-child for that: almost nobody got a job at Google, not even the founders. All they kept were the patents originally purchased from Intel.
