While it probably isn't the first thing you think about, it's not too hard to understand the logic here. A study commissioned by the American Farm Bureau reports that if immigration enforcement is stepped up, food prices will rise by 5-6% and the agricultural industry will lose about $60 billion. I guess it's really tough when you have to pay people the actual minimum wage! That seems like a big loss, though: surely the higher food prices aren't a total loss for the industry.
I was reading about how to fix the US food system the other day, and the first constructive thought I had was about the importance of prices. If there are no incentives for farmers to worry about fertilizers running off of their land and into the Bay (or the Gulf of Mexico, for that matter), they won't do it. If farmers don't pay the full cost of the damage that concentrated animal feeding operations do the environment and the people living nearby, they will certainly continue to do it, just like we continue to abuse parking that is underpriced. And when farmers are paid to produce corn for fuel instead of food, can you blame them when that's what they do?
While higher priced food is a bad thing for consumers, I think we need to accept that the current prices are too low for a number of reasons, including the poor conditions of life for many farm workers. (I'm not saying that the enforcement of immigration is key!) People deserve a decent wage for farm work, and right now they don't get it. It's pretty shocking to hear farmers complain about how farmers clog up the local emergency rooms, when it's their fault the workers lack insurance.