I'd say both with the economy being the overt reason. I don't see why we bother with them actually other than to make work for the employees of the INS. The immigration problem could be squelched by coming down hard on employers who hire workers without green cards. But I guess those employers grease the right palms, the workers get an all expense paid trip back home and then walk back over to their job again.
"So, why'd you miss work last week, Gonzalez?"
"La migra, senor!"
"OK, just don't get picked up again at the height of the season."
So much for immigration laws.