From the NYT:

At the bottleneck of human smuggling here in the Sonoran Desert, illegal immigrants are dying in record numbers as they try to cross from Mexico into the United States in the wake of a new Bush administration amnesty proposal that is being perceived by some migrants as a magnet to cross...

In FY2002, just 13 (thirteen) companies were fined for immigration violations. Reduce the demand, and you'll reduce the supply.