I've seen companies low-ball employees on the order of tens of thousands of dollars. It's basically ancient news now (and the laws in Canada have changed, thank goodness), but when I worked at Corel 20 years ago they would regularly hold people hostage based on visa status (at the time if they were sponsoring the visa, the person couldn't change jobs without losing their visa). Back then, we were all making less than $100K, but educated, experienced immigrants on visa status would often be making less than $50K. As soon as they got permanent residence status, they would be gone -- finally able to negotiate properly. Like I said, Canadian laws have changed and so has Corel management -- I doubt they are doing it now.

We can argue that perhaps the visa was worth the extra money (and for those people, it certainly was), but it's still pretty crap. I'm sure wherever the rules allow it you will find companies (even well known ones) trying to save money in this way.