Although being a non-US citizen, I am appaled by the lack of willingness too hire outside your borders, and the Visa's/green cards needed. I was once told that the US Govt. office of US Immigration and Naturalization Office would rather all hired be a US natural, before a Canadian, Mexican,etc. Clearly this can be viewed as discrimination.
Grant it; not everyone has thee qualifications required to do the job, but as most employer's state - equal opportunity employer, there remains doubt as to what that means.
The US economy is so deprived of workers wanting to work, and most will travel just to have a job, instead of being a "leech"/ dependant on an ever changing Govt. employment insurance system, thus maintaining a sustainable work force.